Information recording medium and information recording and reproducing method

ABSTRACT

A first information recording medium has an electrode layer, and an information recording layer, a multifunctional ultraviolet curing resin material and a fluorocarbon surface-active agent, and ultraviolet curing resin skin layer having no liquid crystal phase on the outer surface of the information recording layer. A second information recording medium has a patterned electrode layer. A third information recording medium has an electrode layer, a photoconductive layer, an information recording layer including a liquid crystal phase and a resin phase, a resin layer, and an electrode layer, wherein at least one of the electrode layers is transparent. A fourth information recording medium further has an insulating layer provided between the photoconductive layer and the information recording layer in the third information recording medium. A fifth information recording medium has an information recording layer provided on an electrode layer. The information recording layer includes a liquid crystal phase containing a dichroic dye, and a resin phase. A sixth information recording medium has an electrode layer, a photoconductive layer, an information recording layer including a liquid crystal phase containing a dichroic dye, and a resin phase, and an electrode layer. At least one of the electrode layers is transparent.

This is a Continuation of Application Ser. No. 08/170,792 filed Dec. 21,1993 (abandoned).

BACKGROUND OF THE INVENTION

The present invention relates to an information recording medium capableof recording, storing and reproducing electrostatic information in theform of visible information by using an ultraviolet curing resinmaterial having a liquid crystal material dispersed and fixed therein.The present invention also relates to an information recording andreproducing method that employs the above-described informationrecording medium.

Liquid crystal display devices have been used as display devices foroffice automation equipment such as word processors, laptop computers,etc. These liquid crystal display devices have a liquid crystal layersandwiched between two transparent substrates, e.g., glass or plasticsubstrates, provided with respective transparent electrode films. Avoltage is applied between the two electrodes by using either simple- oractive-matrix drive, thereby displaying information, e.g., an image.

This type of liquid crystal display device includes typical TN and STNliquid crystal display devices and also those based on dynamicscattering mode, i.e., liquid crystal display devices which operate onthe current effect, and those which utilize the cholesteric-nematicphase transition. Recently, liquid crystal display devices having aliquid crystal material combined with a polymer have also been used. Aliquid crystal display device having a nematic liquid crystal dispersedand fixed in a polymeric resin material displays information accordingto whether it is transparent or opaque by making use of the phenomenonexplained below: The ordinary ray refractive index of the liquid crystalmaterial and the refractive index of the polymeric resin material havepreviously been made equal to each other. When a voltage is applied tothe device to align the molecules of the liquid crystal material in thedirection of the voltage application, the device becomes transparent.When no voltage is applied to the device, the molecules of the liquidcrystal material are irregular in orientation. Consequently, light isscattered at the interface between the liquid crystal and the polymericresin material or in the liquid crystal dispersed and fixed therein.Thus, the liquid crystal display device becomes opaque.

A liquid crystal display device having a nematic liquid crystaldispersed and fixed in a polymeric resin material has the followingadvantageous features: the display area can be increased; the responsetime, particular, the rise time, is short; no polarizer is needed, andhence the light utilization efficiency is high; the viewing angle iswide and uniform; it has flexibility; and so forth. It has recently beenreported that this type of liquid crystal display device is used as alighting control sheet for a window, a projection-type display, etc.This type of liquid crystal display device has an advantage in that thedecay time is as short as 1 ms to 30 ms, which is shorter than that ofTN and STN display devices, which are most commonly used asprojection-type displays and computer displays.

In a conventional liquid crystal display device having a nematic liquidcrystal dispersed and fixed in a polymeric resin material, an AC voltageis applied between two electrodes sandwiching the nematic liquidcrystal, and information is displayed and erased by on/off control ofthe voltage application. In this case, when the application of the ACvoltage is cut off, i.e., when no voltage is applied, the device returnsto the initial transmittance, that is, the opaque state, although thereis a report stating that slight hysteresis is observed in the change oflight transmittance relative to the applied voltage; therefore, there isa difference between the transmittance when the applied AC voltage isrising and the transmittance when the voltage is falling.

A common method of displaying information, e.g., an image, by a liquidcrystal display device is to on/off control a liquid crystal materialsandwiched between two matrix electrodes for each pixel. Otherconventional displaying methods include one that employs an imagewisepatterned electrode, and another wherein when a composite film of apolymer and a liquid crystal is to be formed, a polymeric material ofthe ultraviolet curing type, for example, is used and this is imagewiseirradiated with ultraviolet rays. In these conventional methods,however, fixed information is displayed by on/off control.

Meantime, there are liquid crystal display devices having memory effect.One type of such liquid crystal display device uses cholesteric-nematicphase transition. This type of liquid crystal display device must have asandwich structure in which a liquid crystal material is sandwichedbetween transparent electrodes formed with respective vertical alignmentfilms. In this case, a proper electrode structure is required.

Recently, an information recording medium which uses a polymer dispersedliquid crystal in place of a liquid crystal layer in a liquid crystalcell has been developed. In such an information recording medium, apolymer dispersed liquid crystal is sandwiched between two substrateshaving respective ITO electrodes.

There has also been developed an information recording technique inwhich an information recording medium, which is composed of a substrate,an ITO electrode and a polymer dispersed liquid crystal layer, isdisposed to face a photoelectric sensor composed of an electrode and aphotoconductive layer, thereby forming an information recording system,and information light for exposure is applied to the informationrecording system with a voltage applied between the two electrodes,thereby allowing a voltage corresponding to the information light to beapplied to the polymer dispersed liquid crystal layer, and thusrecording the desired information in the form of liquid crystalalignment in the polymer dispersed liquid crystal layer. In this case,when the liquid crystal dispersed in the resin material is a smecticliquid crystal, particularly large memory effect and orientational orderparameter are obtained. Accordingly, even if the electric field isremoved, the modulated alignment is maintained as it is. Thus, therecorded image can be read even after the information recording mediumhas been allowed to stand for a long time. Since the visible imagerecorded on the medium is erased by heating it to a temperature in thevicinity of the isotropic phase transition temperature of the liquidcrystal, the information recording medium can be reused.

In this type of information recording medium, however, the liquidcrystal oozes from the surface of the information recording layer,causing noise to be generated. Therefore, it is necessary to suppressoozing of the liquid crystal from the information recording layersurface. In addition, if the liquid crystal oozes out, an electrodelayer which is provided on the surface of the information recordinglayer is likely to peel off. Thus, the conventional informationrecording medium is demanded to improve in durability during storage.Furthermore, if an electrode layer is provided on the informationrecording layer by vapor deposition, the surface of the informationrecording layer is also demanded to have durability, i.e., sputteringresistance.

In addition, the conventional information recording medium of the typein which information is recorded in the form of liquid crystal alignmentin the polymer dispersed liquid crystal layer generally suffers from theproblem that a satisfactorily high contrast cannot be obtained betweenrecorded and unrecorded areas of the information recording layer,resulting in lack of signal.

It is a first object of the present invention to provide an informationrecording medium which is free from oozing of the liquid crystal fromthe surface of the information recording layer, superior in durabilityand capable of obtaining an image of high quality without occurrence ofnoise in information recording, and also provide an informationrecording and reproducing method that employs the above-describedinformation recording medium.

It is a second object of the present invention to provide an informationrecording medium of the type described above, which enables informationof high contrast ratio to be obtained.

SUMMARY OF THE INVENTION

The present invention provides an information recording medium having anelectrode layer, and an information recording layer provided on theelectrode layer and including a liquid crystal phase and an ultravioletcuring resin phase. The information recording layer is formed by coatinga surface of the electrode layer with a mixed solution of a liquidcrystal, a multifunctional ultraviolet curing resin material whoseparameter, which is expressed by the average molecular weight divided bythe average functional group, is not larger than 160, and a fluorocarbonsurface-active agent, and then curing the coating by irradiation withultraviolet rays, thereby forming an ultraviolet curing resin skin layerhaving no liquid crystal phase on the outer surface of the informationrecording layer.

In addition, the present invention provides an information recording andreproducing method which employs an information recording medium havingan electrode layer, and an information recording layer provided on theelectrode layer and including a liquid crystal phase and an ultravioletcuring resin phase. The information recording layer is formed by coatinga surface of the electrode layer with a mixed solution of a liquidcrystal, a multifunctional ultraviolet curing resin material whoseparameter, which is expressed by the average molecular weight divided bythe average functional group, is not larger than 160, and a fluorocarbonsurface-active agent, and then curing the coating by irradiation withultraviolet rays, thereby forming an ultraviolet curing resin skin layerhaving no liquid crystal phase on the outer surface of the informationrecording layer. The information recording medium is disposed to face aphotoelectric sensor having a photoconductive layer provided on anelectrode layer, either in or out of contact with each other, therebyforming an information recording system. Information light for exposureis applied to the information recording system with a voltage appliedbetween the respective electrode layers of the information recordingmedium and the photoelectric sensor, thereby aligning the liquid crystalmolecules in the liquid crystal phase in accordance with the appliedinformation light, and thus effecting information recording. Therecorded information is reproduced as visible information by transmittedor reflected light.

In addition, the present invention provides an information recordingmedium having a first electrode layer, an information recording layerprovided on the first electrode layer and including a liquid crystalphase and an ultraviolet curing resin phase, and a second electrodelayer provided on the information recording layer. At least one of theelectrode layers is a transparent electrode layer formed on theinformation recording layer by vapor deposition. The informationrecording layer is formed by coating a surface of the electrode layerwith a mixed solution of a liquid crystal, a multifunctional ultravioletcuring resin material whose parameter, which is expressed by the averagemolecular weight divided by the average functional group, is not largerthan 160, and a fluorocarbon surface-active agent, and then curing thecoating by irradiation with ultraviolet rays, thereby forming anultraviolet curing resin skin layer having no liquid crystal phase onthe outer surface of the information recording layer.

In addition, the present invention provides an information recording andreproducing method which employs an information recording medium havinga first electrode layer, an information recording layer provided on thefirst electrode layer and including a liquid crystal phase and anultraviolet curing resin phase, and a second electrode layer provided onthe information recording layer. At least one of the electrode layers isa transparent electrode layer formed on the information recording layerby vapor deposition, and the information recording layer is formed bycoating a surface of the electrode layer with a mixed solution of aliquid crystal, a multifunctional ultraviolet curing resin materialwhose parameter, which is expressed by the average molecular weightdivided by the average functional group, is not larger than 160, and afluorocarbon surface-active agent, and then curing the coating byirradiation with ultraviolet rays, thereby forming an ultraviolet curingresin skin layer having no liquid crystal phase on the outer surface ofthe information recording layer. According to the information recordingand reproducing method, a voltage is applied in a pattern between thetwo electrode layers, thereby aligning the liquid crystal molecules inthe liquid crystal phase in the pattern of the applied voltage, and thuseffecting information recording. The recorded information is reproducedas visible information by transmitted or reflected light.

The first information recording medium of the present invention retainsthe liquid crystal in the information recording layer so that no liquidcrystal oozes out to the surface of the information recording layer.When this medium is used for an information recording method incombination with a photoelectric sensor, information recording can beeffected on the surface of the information recording layer withoutdisorder. Thus, it is possible to record electrostatic informationwithout unevenness of the recorded image.

In the case of the second information recording medium of the presentinvention, since it is possible to prevent oozing of the liquid crystalfrom the surface of the information recording layer, even when anelectrode layer, e.g., an ITO film, is formed on the informationrecording layer by vapor deposition or the like, the resulting electrodelayer will not be wrinkled or cracked. Thus, it is possible to preventdeterioration of the electrical conductivity. In addition, since theelectrode layer can be provided directly on the information recordinglayer, the gap between the two electrode layers can be made uniform.

In addition, the present invention provides an information recordingmedium having a first electrode layer, a photoconductive layer, aninformation recording layer, a resin layer, and a second electrodelayer, which are successively provided one on top of another. At leastone of the electrode layers is transparent, and the informationrecording layer includes a liquid crystal phase and a resin phase.

In addition, the present invention provides an information recordingmedium having a first electrode layer, a photoconductive layer, atransparent insulating layer, an information recording layer, a resinlayer, and a second electrode layer, which are successively provided oneon top of another. At least one of the electrode layers is transparent,and the information recording layer includes a liquid crystal phase anda resin phase.

In the above-described third and fourth information recording mediums,the information recording layer may contain a fluorocarbonsurface-active agent.

Further, in the third and fourth information recording mediums, theinformation recording layer may be formed by coating a mixed solution ofa liquid crystal and an ultraviolet curing resin material, and thencuring the coating by irradiation with ultraviolet rays, thereby forminga skin layer made only of the ultraviolet curing resin material on theouter surface of the information recording layer.

In addition, the present invention provides an information recording andreproducing method which employs an information recording medium havinga first electrode layer, a photoconductive layer, an informationrecording layer, a resin layer, and a second electrode layer, which aresuccessively provided one on top of another. At least one of theelectrode layers is transparent, and the information recording layerincludes a liquid crystal phase and a resin phase. According to themethod, pattern exposure is carried out with a voltage applied betweenthe two electrode layers, thereby aligning the liquid crystal moleculesin the liquid crystal phase in the pattern of the exposure light, andthus effecting information recording. The recorded information isreproduced as visible information by transmitted or reflected light.

In addition, the present invention provides an information recording andreproducing method which employs an information recording medium havinga first electrode layer, a photoconductive layer, an insulating layer,an information recording layer, a resin layer, and a second electrodelayer, which are successively provided one on top of another. At leastone of the electrode layers is transparent, and the informationrecording layer includes a liquid crystal phase and a resin phase.According to the method, pattern exposure is carried out with a voltageapplied between the two electrode layers, thereby aligning the liquidcrystal molecules in the liquid crystal phase in the pattern of theexposure light, and thus effecting information recording. The recordedinformation is reproduced as visible information by transmitted orreflected light.

The third information recording medium of the present invention canprevent oozing of the liquid crystal from the information recordinglayer by the presence of the resin layer stacked on the informationrecording layer. It is therefore possible to effect informationrecording without occurrence of noise, which would otherwise begenerated by oozing of the liquid crystal. In addition, when anelectrode layer, e.g., an ITO electrode layer, is formed on the resinlayer by vapor deposition or sputtering, even if there is no support,e.g., substrate, on the electrode layer, the required supportingproperties can be satisfactorily obtained. Furthermore, a satisfactorilyhigh hardness is given to the surface of the information recordinglayer, and the information recording medium is improved in durability.In comparison to an information recording medium having an ITO electrodelayer formed directly on the information recording layer by vapordeposition, the third information recording medium has an advantage inthat it is possible to prevent cracking of the ITO electrode layer dueto oozing of the liquid crystal from the information recording layersurface and hence possible to prevent a lowering in electricalconductivity of the ITO electrode layer.

When the information recording layer is formed by using an ultravioletcuring resin material, a skin layer of the ultraviolet curing resinmaterial can be formed as the outer surface layer of the informationrecording layer. Therefore, the information recording layer can containa relatively large amount of liquid crystal. In addition, since thelayer thickness can be reduced, the operating voltage can be set at arelatively low level. Thus, it becomes possible to form a visible imageof high sensitivity, high contrast and high quality.

The fourth information recording medium of the present invention caneliminate the interaction between the photoconductive layer and theinformation recording layer by the presence of the insulating layerprovided between these layers. Accordingly, it is possible to eliminateproblems such as unevenness of the recorded image.

In addition, the present invention provides an information recordingmedium having an electrode layer, and an information recording layerprovided on the electrode layer and including a liquid crystal phase anda resin phase. The liquid crystal phase contains a dichroic dye.

In addition, the present invention provides an information recordingmedium having a first electrode layer, a photoconductive layer, aninformation recording layer, and a second electrode layer, which aresuccessively provided one on top of another. At least one of theelectrode layers is transparent, and the information recording layerincludes a liquid crystal phase and a resin phase. The liquid crystalphase contains a dichroic dye.

In the above-described fifth information recording medium of the presentinvention, a dichroic dye is contained in the information recordinglayer, which includes a liquid crystal phase and a resin phase.Accordingly, in comparison to an information recording medium having aninformation recording layer which includes a liquid crystal phase and aresin phase and contains no dichroic dye, the fifth informationrecording medium has an advantage in that, when no electric charge orelectric field is applied thereto, the transmittance is becomes lowerand the medium becomes opaque, whereas, when electric charge or electricfield is applied thereto, not only the liquid crystal phase (host) butalso the dichroic dye (guest) itself is aligned, and therefore theabsorbances in the two different states can be made even more largelydifferent from each other. Thus, the information recording medium isimproved in contrast.

In the above-described sixth information recording medium, a dichroicdye is contained in the information recording layer, which includes aliquid crystal phase and a resin phase. In addition, the medium has aphotoconductive layer. Therefore, the information recording medium iscapable of information recording by itself.

In the first to sixth information recording mediums of the presentinvention, the information recording layer is composed of a liquidcrystal phase and a resin phase, and electro-optic effect can readily beobtained. Accordingly, analog information can be recorded and stored. Inaddition, since the information recording layer can be made uniform andreduced in thickness by coating technique, an information recordingmedium of large area can be produced, and it is possible to record andreproduce an image of high resolution. In addition, by making therefractive indices of the liquid crystal and resin phases in theinformation recording layer approximately equal to each other, theinformation recording layer can be selectively made opaque andtransparent as follows: When no electric field is applied thereto byinformation electric charge, the information recording layer is opaquedue to light scattering, whereas, when an electric field is applied tothe information recording layer, the molecules in the liquid crystalphase are aligned, thus enabling the information recording region tobecome transparent. No polarizer is needed when the recorded informationis reproduced, and hence the optical system required for reading can besimplified.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows first and second information recordingmediums of the present invention, in which (a) is a sectional view ofthe first information recording medium, and (b) is a sectional view ofthe second information recording medium.

FIG. 2 schematically shows an information recording system using eitherthe first or fifth information recording medium of the presentinvention.

FIG. 3 is a view for explanation of a method of reproducing informationrecorded on the first and fifth information recording mediums of thepresent invention.

FIG. 4 schematically shows third and fourth information recordingmediums of the present invention, in which (a) is a sectional view ofthe third information recording medium, and (b) is a sectional view ofthe fourth information recording medium.

FIG. 5 is a view for explanation of a method of recording information onthe third information recording medium of the present invention.

FIG. 6 is a view for explanation of a method of reproducing informationrecorded on the third information recording medium of the presentinvention.

FIG. 7 schematically shows fifth and sixth information recording mediumsof the present invention, in which (a) is a sectional view of the fifthinformation recording medium, and (b) is a sectional view of the sixthinformation recording medium.

FIG. 8 is a view for explanation of a method of recording information onthe sixth information recording medium of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First of all, the first information recording medium of the presentinvention will be described below. FIG. 1(a) is a sectional viewschematically showing the first information recording medium. In thefigure, reference numeral 3 denotes an information recording medium, 11an information recording layer, 13 an electrode layer, and 15 asubstrate.

The information recording layer 11 has a structure which includes aliquid crystal phase and a resin phase. Examples of liquid crystalsusable in the present invention include a smectic liquid crystal, anematic liquid crystal, and a mixture of these liquid crystals. However,it is preferable to use a smectic liquid crystal or a mixture of smecticand nematic liquid crystals from the viewpoint of retaining the liquidcrystal alignment and holding the recorded information permanently, thatis, from the viewpoint of memory effect.

Examples of smectic liquid crystals usable in the present invention areas follows: cyanobiphenyl, cyanoterphenyl and phenylester liquidcrystals, which present smectic phase at ordinary temperature (25°) andin which the end group of a liquid crystalline substance has a longcarbon chain; liquid crystal substances that present smectic A phase,e.g., fluorine liquid crystal; liquid crystal substances that presentsmectic C phase, which are used as ferroelectric liquid crystals orantiferroelectric liquid crystals; and liquid crystal substances thatpresent smectic H, G, E or F phase. Smectic liquid crystals are superiorin memory effect, that is, the ability to retain the liquid crystalalignment after information has been recorded, and to hold the recordedinformation permanently.

A nematic liquid crystal mixed with a smectic liquid crystal is onewhich shows nematic phase at ordinary temperature (25° C.). It ispossible to use known nematic liquid crystals, for example, Schiff'sbase, azoxy, azo, phenyl benzoate, cyclohexyl phenyl ester, biphenyl,terphenyl, phenylcyclohexane, phenylpyridine, phenyloxazine, polycyclicethane, phenylcyclohexene, cyclohexylpyrimidine, phenyl and tolan liquidcrystals. It should be noted that it is preferable to select a liquidcrystal material having higher anisotropy of refractive index with aview to obtaining a higher contrast. It is preferable to mix together anematic liquid crystal and a smectic liquid crystal in a weight ratio offrom 5:95 to 20:80. If the amount of nematic liquid crystal is less than5% by weight, the variation of light transmittance is large, whereas, ifit exceeds 20% by weight, the memory effect is degraded, and thevariation of light transmittance also becomes large. By using a mixedphase of nematic and smectic liquid crystals, the liquid crystaldistribution in the information recording layer can be made uniform andthe transmittance variation can be minimized in comparison to aninformation recording layer formed of a nematic or smectic liquidcrystal alone, although the reason for this is not clear.

Examples of materials which are preferable to use for forming the resinphase are ultraviolet curing resin materials which are compatible with aliquid crystal material or a common solvent therewith in the form of amonomer or an oligomer. Examples of such ultraviolet curing resinmaterials are multifunctional ultraviolet curing resin materials whoseparameter, which is expressed by the average molecular weight divided bythe average functional group, is not larger than 160, preferably in therange of 80 to 150, such as acrylic and methacrylic esters.

Specific examples of the above-described ultraviolet curing resinmaterials include multifunctional monomers and multifunctional urethaneand ester oligomers, e.g., dipentaerythritol hexaacrylate,trimethylolpropane triacrylate, polyethylene glycol diacrylate,polypropylene glycol diacrylate, isocyanuric acid (ethylene oxidemodified) triacrylate, dipentaerythritol pentaacrylate,dipentaerythritol tetraacrylate, neopentyl glycol diacrylate, hexanedioldiacrylate, etc. When an information recording layer is formed by usingan ultraviolet curing resin as a resin material, the resultinginformation recording layer has such a structure that the surface of thelayer is covered with the ultraviolet curing resin material, and theinside of the layer is filled with the liquid crystal phase and theresin particle phase. The present invention is made on the basis of thefinding that when a multifunctional ultraviolet curing resin materialwhose parameter, which is expressed by the average molecular weightdivided by the average functional group, is not larger than 160 is usedas a resin phase forming material, it is possible to form an informationrecording layer which is superior in durability and free from oozing ofthe liquid crystal in comparison to an information recording layerformed using an ultraviolet curing resin material in which theabove-described parameter exceeds 160.

In addition, by making the refractive indices of the liquid crystal andresin phases in the information recording layer approximately equal toeach other, the information recording layer can be selectively madeopaque and transparent as follows: When no electric field is appliedthereto, the information recording layer is opaque due to lightscattering, whereas, when an electric field is applied to theinformation recording layer, the molecules in the liquid crystal phaseare aligned, thus enabling the information recording region to becometransparent. No polarizer is needed when the recorded information isreproduced, and hence the optical system required for reading can besimplified.

As to the solvent, any common solvent can be used. However, it ispreferable to use a solvent whose relative evaporation rate for n-butylacetate is smaller than 2, for example, hydrocarbon solvents representedby xylene, halogenated hydrocarbon solvents represented by chloroform,alcohol derivative solvents represented by methyl cellosolve, and ethersolvents represented by dioxane.

Examples of photo-curing agents usable in the present invention are2-hydroxy-2-methyl-1-phenylpropane-1-one ("Darocure 1173", manufacturedby Ciba-Geigy Ltd.), 1-hydroxycyclohexyl phenyl ketone ("Irgacure 184",manufactured by Ciba-Geigy Ltd.),1-(4-isopropylphenyl)-2-hydroxy-2-methylpropane-1-one ("Darocure 1116",manufactured by Ciba-Geigy Ltd.), benzyl dimethyl ketal ("Irgacure 651",manufactured by Ciba-Geigy Ltd.), 2-methyl-1-4-(methylthio)phenyl!-2-morpholinopropanone-1 ("Irgacure 907",manufactured by Ciba-Geigy Ltd.), a mixture of 2,4-diethylthioxanthone("Kayacure DETX", manufactured by Nippon Kayaku Co., Ltd.) andp-dimethylamino ethyl benzoate ("Kayacure EPA", manufactured by NipponKayaku Co., Ltd.), and a mixture of isopropylthioxanthone ("Quantacure.ITX", manufactured by Wordblekinsop Co., Ltd.) and p-dimethylamino ethylbenzoate. However, 2-hydroxy-2-methyl-1-phenylpropane-1-one, which isliquid, is particularly preferable from the viewpoint of compatibilitywith a liquid crystal and a resin material, e.g., a polymer formingmonomer or oligomer.

It is preferable to use a liquid crystal and a resin material in suchproportions that the liquid crystal content in the information recordinglayer is 10% to 90% by weight, more preferably 40% to 80% by weight. Ifthe liquid crystal content is less than 10% by weight, the contrastratio is low even when the molecules in the liquid crystal phase arealigned by information recording, whereas, if the liquid crystal contentexceeds 90% by weight, unfavorable phenomena such as oozing of theliquid crystal occur, causing unevenness of the recorded image. Ingeneral, by allowing the information recording layer to contain a largeamount of liquid crystal, the contrast ratio can be improved, and theoperating voltage can be lowered. In doing so, however, the dispersionof the liquid crystal phase may become uneven, causing unevenness oftransmittance, which generates noise in information recording.

Further, in the present invention, a fluorocarbon surface-active agentmay be added for the purpose of maintaining the wetting properties withrespect to the electrode layer and forming a skin layer made only of aresin material on the surface of the information recording layer.

Examples of fluorocarbon surface-active agents usable for this purposeinclude Fluorad FC-430 and FC-431 (manufactured by Sumitomo 3M (K.K.)),N-(n-propyl)-N-(β-acryloxyethyl)-perfluorooctyl sulfonamide (EF-125M,manufactured by Mitsubishi Material Co., Ltd.),N-(n-propyl)-N-(β-methacryloxyethyl)-perfluorooctyl sulfonamide(EF-135M, manufactured by Mitsubishi Material Co., Ltd.),perfluorooctanesulfonic acid (EF-101, manufactured by MitsubishiMaterial Co., Ltd.), perfluorocaprylic acid (EF-201, manufactured byMitsubishi Material Co., Ltd.), and N-(n-propyl)-N-perfluorooctanesulfonamide ethanol (EF-121, manufactured by Mitsubishi Material Co.,Ltd.), and further include EF-102, EF-103, EF-104, EF-105, EF-112,EF-121, EF-122A, EF-122B, EF-122C, EF-122A3, EF-123A, EF-123B, EF-132,EF-301, EF-303, EF-305, EF-306A, EF-501, EF-700, EF-201, EF-204, EF-351,EF-352, EF-801, EF-802, EF-125DS, EF-1200, EFL102, EF-L155, EF-L174 andEF-L215, which are manufactured by Mitsubishi Material Co., Ltd.). It isalso possible to use 3-(2-perfluorohexyl)ethoxy-1,2-dihydroxypropane(MF-100, manufactured by Mitsubishi Material Co., Ltd.),N-n-propyl-N-2,3-dihydroxypropylperfluorooctyl sulfonamide (MF-110,manufactured by Mitsubishi Material Co., Ltd.),3-(2-perfluorohexyl)ethoxy-1,2-epoxypropane (MF-120, manufactured byMitsubishi Material Co., Ltd.),N-n-propyl-N-2,3-epoxypropylperfluorooctyl sulfonamide (MF-130,manufactured by Mitsubishi Material Co., Ltd.), perfluorohexyl ethylene(MF-140, manufactured by Mitsubishi Material Co., Ltd.), N-3-trimethoxysilyl)propyl! perfluoroheptyl carboxylic acid amide (MF-150,manufactured by Mitsubishi Material Co., Ltd.), N-3-trimethoxysilyl)propyl! perfluoroheptyl sulfonamide (MF-160,manufactured by Mitsubishi Material Co., Ltd.), etc. The fluorocarbonsurface-active agent is used in the proportion of 0.1% to 20% by weightto the total amount of liquid crystal and resin material used. Ifnecessary, a leveling agent may be added to the mixed solution toimprove the coatability of the solution and to thereby obtain excellentsurface properties.

Next, the steps of a method for forming the information recording layerwill be explained in order:

(1) A liquid crystal, a resin material, a photo-polymerizationinitiator, a fluorocarbon surface-active agent are mixed with a solventwhose relative evaporation rate for n-butyl acetate is smaller than 2,thereby preparing a mixed solution having a solid content of 10% to 60%by weight. The solvent dilution is carried out so that the viscosity ofthe resulting solution is in the range of 1 to 500 cps (20° C.),preferably 10 to 200 cps (20° C.). If the viscosity is excessively low,the coating solution undesirably flows, making it impossible to maintainthe required film thickness after the coating process. If the viscosityis excessively high, it is difficult to effect leveling. In addition,the constituent materials are dissolved on heating at a temperature notlower than the temperature at which the liquid crystal maintains theisotropic phase, preferably in the range of ±10° C. of the isotropicphase transition temperature. During the preparation of the solution, agel formed from the ultraviolet curing resin material and foreignmatter, which are present in the solution, are removed by filtration. Agel or foreign matter left in the solution causes noise when informationis recorded on the resulting information recording medium.

It should be noted that if the solvent is evaporated to dryness when themixed solution is heated at a temperature not lower than the isotropicphase temperature in the stage of preparation thereof, phase separationoccurs in the mixed solution. Thus, the information recording layer ofthe present invention cannot be formed with the mixed solution that isin the above-described state. Therefore, it is preferable to use asolvent whose relative evaporation rate for n-butyl acetate is smallerthan 2. If the relative evaporation rate is larger than 2, evaporationtakes place at an excessively high rate, causing the above-describedproblem. In general, it is possible to use even a solvent whose R is inthe range of 0.3 to 1 as long as it can be dissolved on heating at atemperature not higher than 70° C. For example, xylene (R=0.7) ispreferably used. In a case where heating at 70° C. or higher is neededfor dissolution, a solvent whose R is less than 0.3, e.g., cyclohexane(R=0.2), may be used.

(2) Next, the mixed solution is coated to a uniform film thickness onthe electrode layer under room temperature conditions by a coatingmethod using a spin coater, a bar coater, a blade coater, or a rollcoater.

(3) The solvent is removed by evaporation with the coating layermaintained at a temperature higher than the temperature at which theliquid crystal maintains the isotropic phase, preferably in the range of±10° C. of the isotropic phase transition temperature. If thetemperature of the coating layer is lower than the isotropic phasetransition temperature by 10° C. or more, large phase separation occursbetween the liquid crystal and the ultraviolet curing resin material,thus giving rise to problems. That is, the liquid crystal domain growsexcessively, preventing a skin layer from being formed completely overthe surface of the information recording layer, so that the liquidcrystal will ooze out. In addition, the ultraviolet curing resinmaterial is matted, so that it becomes difficult to take in informationaccurately. Further, there are cases where the ultraviolet curing resinmaterial cannot even retain the liquid crystal and hence no informationrecording layer is formed. If the temperature of the coating layer ishigher than the isotropic phase transition temperature by 10° C. ormore, the phase separation between the liquid crystal phase and theresin phase in the information recording layer becomes unclear, althoughthe reason for this is not clear.

(4) With a view to removing the solvent completely, the drying treatmentis preferably carried out in two steps, that is, hood drying and vacuumdrying. By doing so, it is possible to prevent the surface of theinformation recording layer from becoming uneven, which would otherwisebe caused by the flow of air, and hence possible to prevent occurrenceof interference fringes.

(5) Next, the coating layer, which has been dried, is cured byirradiation with ultraviolet rays by using an UV lamp. In this process,infrared radiation is shielded, and ultraviolet radiation in which aradiation component in the range of 200 nm to 400 nm in wavelength is 1%or more is applied to the coating layer at an energy of not lower than0.1 mJ/cm². By doing so, it is possible to obtain an informationrecording layer which is excellent in the phase separation between theliquid crystal phase and the resin phase.

By the above-described information recording layer forming process, askin layer having a thickness which accounts for 0.01% to 30% of thethickness of the information recording layer can be formed on thesurface of the information recording layer, and the inside of theinformation recording layer has a structure in which the liquid crystalphase, which forms a continuous layer, is filled with resin particleshaving a primary particle diameter of 0.03 μm to 0.6 μm. If amultifunctional ultraviolet curing resin material whose parameter, whichis expressed by the average molecular weight divided by the averagefunctional group, is not larger than 160 is used as an ultravioletcuring resin material, it is possible to form an information recordinglayer whose surface skin layer has superior durability.

By virtue of the presence of the durable skin layer formed on theinformation recording layer surface, it is possible to increase theproportion of liquid crystal used in the information recording layer,and there is no oozing of the liquid crystal to the surface of theinformation recording layer. Thus, it is possible to prevent a recordedimage from being disordered by oozing of the liquid crystal, which wouldotherwise occur. Thus, an image of high quality can be obtained.

It should be noted that if the phase separation between the liquidcrystal phase and the resin phase are incomplete in the fine structureinside the information recording layer, the desired contrast cannot beobtained. In addition, if the phase separation is incomplete, theresistance of the information recording layer itself lowers undesirably.Accordingly, when information recording is effected by the action of anelectric field based on electrostatic information using a photoelectricsensor, the required voltage cannot effectively be applied to the liquidcrystal phase in the information recording layer. Consequently, thedrive of the liquid crystal becomes slow, causing a reduction in thesensitivity. Furthermore, if the phase separation is incomplete, whenthe ultraviolet curing resin material is irradiated by a UV lamp thatemits radiation containing infrared rays, nonuniform shrinkage is causedby unnecessary heating, which gives rise to a serious problem that theresulting information recording layer is neither uniform norhomogeneous, which is fatal to an information recording medium.

(6) The information recording layer thus formed has an average layerthickness in the range of 1 μm to 30 μm. If the layer thickness isexcessively large, the operating voltage rises. In general, when it isdesired to raise the sensitivity, the layer thickness should be reduced,whereas, when the contrast is desired to become higher, the layerthickness should be increased. For the information recording layer to besuperior in both sensitivity and contrast ratio, the layer thicknessshould preferably be in the range of 3 μm to 20 μm, more preferably 5 μmto 10 μm. With such a layer thickness, it is also possible to lower theoperating voltage while maintaining the high contrast.

The thickness of the skin layer provided on the information recordinglayer may be in the range of 0.01% to 50% of the thickness of theinformation recording layer. If the skin layer is excessively thin, theliquid crystal oozes out, causing noise when information is recorded onthe surface thereof by using a photoelectric sensor (described later).Therefore, the thickness of the skin layer is preferably set in therange of 0.01% to 30% of the thickness of the information recordinglayer. The thickness of the skin layer can be properly adjustedaccording to the kind of ultraviolet curing resin material used, theirradiation dose of ultraviolet rays, the amount of fluorocarbonsurface-active agent added, and so forth, although the reason for thisis not clear.

In the first information recording medium of the present invention, theinformation recording layer needs to be formed by coating so as to havean accurate and uniform thickness. In this regard, the above-describedmethod enables formation of an information recording layer having anaccurate and uniform thickness. That is, as to the uniformity of layerthickness, when the thickness is in the range of 5 μm to 10 μm, thesurface roughness Ra of the information recording layer can be heldwithin 200 Å, and there is no contrast unevenness. In addition, noshading phenomenon occurs during information recording.

In this type of polymer dispersed liquid crystal, it is generallyconsidered that the definition thereof depends more on the domain sizeof the liquid crystal than on the layer thickness. However, in aninformation recording layer in which the liquid crystal content isrelatively high and the resin material forms a resin phase in the formof particles as in the case of the information recording layer of thepresent invention, it is unnecessary to give much consideration to thedomain size of the liquid crystal as in the case of the conventionalpolymer dispersed liquid crystal having a relatively low liquid crystalcontent. Therefore, it is possible to readily provide an informationrecording medium of high sensitivity and high contrast ratio.

The electrode 13 may be either transparent or opaque. Any material whichstably gives a resistivity of not higher than 10⁶ ohm-cm can be used forthe electrode 13. Examples of such material are a thin metallicconductive film, an inorganic metallic oxide conductive film, e.g.,indium-tin oxide (ITO), and an organic conductive film, e.g., quaternaryammonium salt, and so forth. The electrode 13 is formed by vapordeposition, sputtering, CVD, coating, plating, dipping, electrolyticpolymerization, etc. The thickness of the electrode layer 13 needs to bechanged depending upon the electrical characteristics of the materialthereof and the level of voltage applied to record information. Forexample, the thickness is about from 100 Å to 3,000 Å in the case of anITO film. The electrode 13 may be formed either on the whole areabetween the substrate and the information recording layer or inconformity with a pattern in which the information recording layer isformed.

The substrate 15 may be either transparent or opaque. The substrate 15supports the information recording medium having the shape of card,film, tape, disk or the like so as to provide the required strength.Accordingly, the substrate 15 need not be provided if the informationrecording layer itself has supporting properties, and there are nospecific restrictions on the thickness and material of the substrate 15,provided that it is sufficiently strong to support the informationrecording layer. Examples of usable materials are a flexible plasticfilm, or a rigid material such as glass, plastic sheet, card, etc. Morespecifically, when the information recording medium has the shape of aflexible film, tape, disk or card, a flexible plastic film is used. Whena certain strength is required, a rigid inorganic material, e.g., sheetor glass, is used.

It should be noted that when the recorded information is reproduced bytransmitted light, the electrode layer 13 and substrate 15 must betransparent. In such a case, anti-reflection properties may be impartedto the substrate by stacking a layer having anti-reflection effect onthe surface of the substrate 15 which is remote from the electrode layer13, or by adjusting the thickness of the transparent substrate to alevel at which anti-reflection effect is obtainable, or by combiningtogether these two measures, according to need.

Next, a method of recording information on the first informationrecording medium of the present invention will be explained.

Recording of information on the information recording medium of thepresent invention may be effected by using a photoelectric sensor, heat,laser, corona charging, or other similar recording method. However, itis preferable to effect information recording by using a photoelectricsensor.

As shown in FIG. 2, a photoelectric sensor 1 usable for the informationrecording has an electrode layer 13" and a photoconductive layer 14,which are stacked on a transparent substrate 15 in the mentioned order.The electrode layer 13" is formed of the same material and by the samemethod as in the case of the electrode layer 13 described above inconnection with the first information recording medium. When theelectrode layer 13" is formed by sputtering, it is possible to controlthe injection of electric charge into the photoconductive layer 14 fromthe electrode layer 13" by heating the electrode layer 13" after it hasbeen formed, and thereby changing the crystalline structure.

The photoconductive layer 14 may have a single-layer structure which hasboth a function of generating electric charge according to informationlight applied and a charge transport function, or a double-layeredstructure including a charge generation layer and a charge transportlayer, which are stacked in the mentioned order on the electrode layer.The photoconductive layer generally functions such that when it isirradiated with light, photocarriers (electrons or holes) are generatedin the irradiated portion and these carriers are movable across thewidth of the layer. The photoconductive layer exhibits the effectparticularly remarkably in the presence of an electric field. Such aphotoelectric sensor is described, for example, in Japanese PatentApplication No. 04-287983 (1992). The photoelectric sensor described inthis publication has such a function that an electric field or electriccharge, which is given to an information recording medium when thephotoelectric sensor is irradiated with light, is amplified with timeduring the light irradiation. In addition, even after the termination ofthe light irradiation, when the voltage is continuously applied, thephotoelectric sensor sustains the electrical conductivity andcontinuously gives the electric field or the electric charge to theinformation recording medium.

FIG. 2 shows an information recording system that incorporates aphotoelectric sensor. In the figure, reference numeral 1 denotes aphotoelectric sensor, 3 an information recording medium, 13" anelectrode of the photoelectric sensor, 14 a photoconductive layer, 11 aninformation recording layer, 13 an electrode of the informationrecording medium, 15 a substrate, 19 a spacer, 21 a light source, 22 ashutter having a driving mechanism, 23 a pulse generator (power source),and 24 a camera obscura.

In information recording, when information light is incident on theinformation recording system from the light source 21 with a voltageapplied between the electrodes 13 and 13' from the power source (pulsegenerator) 23, photocarriers are generated in the photoconductive layer14 at the region where the light is incident, and the photocarriers moveas far as the interface of the photoconductive layer 14 on the sidethereof which is closer to the information recording layer 11 by theaction of an electric field formed by the two electrodes 13 and 13',causing redistribution of the voltage. As a result, the molecules in theliquid crystal phase in the information recording layer 11 are alignedin the pattern of information light, thereby recording the desiredinformation. Although in the illustrated system the electrode 13" of thephotoelectric sensor 1 is used as a positive electrode, while theelectrode 13 of the information recording medium 3 is used as a negativeelectrode, the polarities may be set according to the electric dischargecharacteristics of the photoelectric sensor used, as a matter of course.

Since some liquid crystal materials operate at a relatively low voltage,when the level of applied voltage is to be set, it is preferable toproperly set the voltage distribution among the photoelectric sensor,the air gap and the information recording medium so that the voltagedistributed to the information recording layer will fall in theoperating voltage range of the liquid crystal used. Informationrecording that is effected by a photoelectric sensor enables planaranalog recording and makes it possible to align the molecules in theliquid crystal phase at the electrostatic charge level. Therefore, it ispossible to obtain high resolution as in the silver halide photography,and it is also possible to retain the exposure light pattern in the formof a visible image by the molecular alignment in the liquid crystalphase.

To record information on the first information recording medium of thepresent invention, a method that uses a camera or a recording methodthat uses laser may be employed. The recording method by a camera usesthe information recording medium as a recording member in place of aphotographic film used in an ordinary camera. Either an optical orelectrical shutter can be used for this camera. It is also possible toconduct color photography by using a color filter and prisms by whichlight information is separated into R, G and B light components andtaken out in the form of parallel rays, and forming one frame from threeinformation recording mediums for R, G and B light components or fromone set of R, G and B images recorded on one plane.

In the recording method by laser, argon laser (514 nm, 488 nm),helium-neon laser (633 nm) or semiconductor laser (780 nm, 810 nm, etc.)may be used as a light soure. Laser exposure corresponding to an imagesignal, character signal, code signal or line drawing signal isperformed by scanning. Analog recording such as recording of an image iseffected by modulating the intensity of laser light, whereas digitalrecording such as recording of characters, code or line drawing iseffected by on/off control of laser light. An image that consists ofhalftone dots is formed by on/off controlling laser light through a dotgenerator.

Next, the second information recording medium of the present inventionwill be explained. FIG. 1(b) is a sectional view of the secondinformation recording medium according to the present invention. In thefigure, reference numeral 13' denotes a patterned electrode layer, andthe same reference numerals as those in FIG. 1(a) denote the samecontents.

The second information recording medium is formed by additionallyproviding a patterned electrode layer 13' on the surface of theinformation recording layer of the first information recording medium.The electrode layer 13' can be formed by using a material selected fromamong those mentioned for the above-described electrode layer 13. It ispreferable to provide an indium-tin oxide (ITO) layer, for example, inthe desired pattern by sputtering or vapor deposition. It is preferablethat at least one of the electrode layers 13 and 13' should betransparent.

If the information recording layer is formed by using an ultravioletcuring resin material whose parameter, which is expressed by the averagemolecular weight divided by the average functional group, exceeds 160,even when the resin material is cured and a skin film is thus formed onthe surface of the information recording layer, the liquid crystal islikely to ooze to the surface of the layer. Accordingly, even if ITO,for example, is stacked on the surface of the information recordinglayer by sputtering or vapor deposition, the ITO film will be cracked,resulting in a lowering of the electrical conductivity. However, byusing a multifunctional ultraviolet curing resin material whoseparameter, which is expressed by the average molecular weight divided bythe average functional group, is not larger than 160, it is possible toform an information recording layer whose surface has sputteringresistance. Accordingly, even if ITO, for example, is provided directlyon the surface of the information recording layer by vacuum depositionor sputtering, the electrode layer will not be cracked, and there is nolikelihood that the electrical conductivity will lower.

Recording of information on the second information recording medium iseffected by aligning the molecules in the liquid crystal layer inaccordance with the patterned electrode layer 13' by applying a voltagebetween the electrode layers 13 and 13', thereby enabling recording inaccordance with the desired pattern.

The arrangement may be such that the electrode layers 13 and 13' areformed in a matrix to record information in a pattern by controlling thevoltage applied between the electrode layers 13 and 13' so that thedesired pattern is formed.

The arrangement may also be such that electrodes 13 and 13' are entirelyprovided on both sides of the information recording layer, and with alow voltage applied between the electrodes 13 and 13', the informationrecording layer is heated in a pattern by using laser light or the likeso that the operating voltage at the heated regions is lowered to alevel substantially equal to the applied voltage, thereby recording thepattern of the laser light.

Electrostatic information recorded on either the first or secondinformation recording medium is reproduced as follows: When theinformation is reproduced by transmitted light, as shown in FIG. 3, inthe information recording region, light A is transmitted because theliquid crystal molecules are aligned in the direction of the electricfield, whereas, in the region where no information has been recorded,light B is scattered, thus providing a contrast with the informationrecording region. Information that is recorded by the liquid crystalalignment is visible information which can be read by visual observationusing transmitted light, and it can also be read in the form of anenlarged image by using a projector. When laser scanning or CCD is usedto read the recorded information by transmitted light, the informationcan be read with high accuracy. It should be noted that occurrence ofscattered light can be prevented by using a Schlieren optical system, ifnecessary. It is also possible to read the recorded information byreflected light. When the contrast is a matter of great concern, areflecting layer should be provided on any of the layers.

In addition, the first and second information recording mediums are cutinto an appropriate size in the width direction of the layers accordingto each particular use application. Accordingly, the interior of theinformation recording layer is exposed at each cut surface, so that theliquid crystal phase may ooze out during storage. If the oozingphenomenon occurs, accurate information recording cannot be effected atthe end portions of the information recording medium. To prevent theoccurrence of this problem, it is preferable to stack a resin layersimilar to the above on each cut surface by coating or laminating afterthe information recording medium has been cut into an appropriateconfiguration, thereby protecting the cut surfaces.

The first and second information recording mediums are designed torecord electrostatic information in a visible form by the liquid crystalalignment. By properly selecting a combination of a liquid crystal and aresin material, these information recording mediums are endowed withmemory effect that makes it possible to retain information that has oncebeen recorded in a visible form by the liquid crystal alignment. Therecorded information can be erased by heating the medium to a hightemperature near the isotropic phase transition temperature. Thus, themedium can be reused for information recording.

The first and second information recording mediums and the informationrecording and reproducing method employing these mediums will beexplained below more specifically by way of Examples 1 to 4 andComparative Example 1. In these Examples, the term "parts" means partsby weight.

EXAMPLE 1!

The following constituent materials were uniformly dissolved in 105parts of xylene to prepare a coating solution:

    ______________________________________                                        Dipentherythritol hexaacrylate                                                                            40    parts                                       (DPHA, M-400, manufactured by Toa Gosei Chemical                              Industry                                                                      Co., Ltd., molecular weight/functional group = 117)                           Photo-curing initiator      2     parts                                       (2-hydroxy-2-methyl-1-phenylpropane-1-one, Darocure 1173,                     manufactured by Ciba-Geigy Ltd.)                                              Smectic liquid crystal      60    parts                                       (S-6, manufactured by BDH)                                                    Fluorocarbon surface-active agent                                                                         3     parts                                       (Fluorad FC-430, manufactured by Sumitomo 3M)                                 ______________________________________                                    

The resulting solution was coated by using a blade coater on the ITOfilm side of a glass substrate (1.1 mm in thickness) having an ITO filmformed thereon to a thickness of about 2,000 Å by sputtering. The wetcoating was dried for 3 minutes at 50° C. and then vacuum-dried for 2minutes at 50° C. Immediately thereafter, the dry film was irradiatedwith ultraviolet rays at 500 mJ/cm² to cure the resin material, therebypreparing a first information recording medium of the present invention.The thickness of the information recording layer was 6 μm.

A cross-section of the information recording layer was dried after theliquid crystal was extracted with hot methanol, and then the internalstructure of the information recording layer was observed with ascanning electron microscope (S-800, manufactured by Hitachi, Ltd.;magnification of 10,000). As a result, it was revealed that the surfaceof the information recording layer was covered with the ultravioletcuring resin material having a thickness of 0.6 μm and the inside of thelayer had a structure in which the liquid crystal phase that formed acontinuous layer was filled with the resin particle phase having aparticle diameter of 0.1 μm.

When an ITO film was formed in a pattern on the cured informationrecording layer by sputtering to form an upper electrode, it waspossible to form the ITO film with a thickness of about 1,000 Å. Thus, asecond information recording medium according to the present inventionwas prepared.

Lead wires were attached to the two electrodes of the second informationrecording medium, and a DC voltage of 400 V was applied between theterminals of the electrodes for 0.1 sec. Before the application of thevoltage, the transmittance of light of 633 nm was 40%, whereas after thevoltage application, the transmittance was 80%. The transparent statewas held for more than 1 year at room temperature. Thus, the informationrecording medium exhibited excellent memory properties. Next, theinformation recording medium which had already been subjected to thevoltage application was placed on a hot plate at 60° C. for 10 sec., andimmediately thereafter, the medium was cooled down to room temperature.In consequence, the whole medium returned to the scattering state beforethe voltage application without oozing of the liquid crystal, so that itbecame capable of being reused.

EXAMPLE 2!

First and second information recording mediums of the present inventionwere prepared in the same way as in Example 1 except that thedipentaerythritol hexaacrylate in Example 1 was replaced by the sameamount of an acrylate, TPA-330, trade name (molecular weight/functionalgroup=157; manufactured by Nippon Kayaku Co., Ltd.). When theinformation recording mediums were tested in the same way as in Example1, the same results as those in Example 1 were obtained.

EXAMPLE 3!

First and second information recording mediums of the present inventionwere prepared in the same way as in Example 1 except that thedipentaerythritol hexaacrylate in Example 1 was replaced by the sameamount of trimethylolpropane triacrylate (TMPTA; molecularweight/functional group=99; manufactured by Nippon Kayaku Co., Ltd.).When the information recording mediums were tested in the same way as inExample 1, the same results as those in Example 1 were obtained.

EXAMPLE 4!

On a glass substrate having a thickness of 1.1 mm and thoroughlycleaned, an ITO film having a thickness of 1,000 Å was deposited by EBevaporation to obtain an electrode layer.

The surface of the electrode was coated with a coating solution in 0.4sec. by a spinner at 1,400 rpm. The coating solution was prepared bymixing together 3 parts by weight of a fluorenone-azo pigment having thefollowing structure as a charge generating substance, 1 part by weightof a polyester resin material (Vylon 200, manufactured by Toyobo Co.,Ltd.), 98 parts by weight of 1,4-dioxane, and 98 parts by weight ofcyclohexanone and shaking the mixture for 6 hours in a paint shaker.##STR1##

Thereafter, drying was carried out for 1 hour at 100° C. Thus, a chargegeneration layer having a thickness of 3,000 Å was stacked on theelectrode.

The surface of the charge generation layer was coated with a coatingsolution in 0.3 msec. by a spinner at 300 rpm. The coating solution wasprepared by mixing together 25 parts by weight of a para-dimethylstilbene having the following structure as a charge transport substance,5 parts by weight of a polystyrene resin material (HRM-3, manufacturedby Denki Kagaku Kogyo K.K.), 102 parts by weight of1,1,2-trichloroethane, and 68 parts by weight of dichloromethane.##STR2##

Thereafter, drying was carried out for 2 hours at 80° C., therebystacking a charge transport layer on the charge generation layer, andthus obtaining a photoelectric sensor having a photoconductive layer of20 μm in thickness.

The photoelectric sensor and the first information recording mediumprepared in Example 1 were disposed to face each other across an air gapof 10 μm defined by a spacer 19 of polyimide film, thereby forming aninformation recording system as shown in FIG. 2.

A DC voltage of 850 V was applied between the respective electrodes ofthe photoelectric sensor and the information recording medium for 0.05sec., and at the same time, exposure was carried out by projecting agray scale from the photoelectric sensor side for 1/30 sec. with animaging camera (RB67, manufactured by Mamiya Camera Co., Ltd.). Afterthe exposure, the information recording medium was taken out. When theinformation recording medium was observed by transmitted light, thetransmittance in the light-transmitting portions was 80%, and recordregions comprising the light-transmitting portions corresponding to thegray scale were observed.

Next, the information recorded on the information recording medium wasread with a film scanner (LS-3500, manufactured by Nikon Corporation),and the read information was output by using a sublimation transferprinter (SP-5500, manufactured by JVC). As a result, a favorable printcorresponding to the gray scale was obtained.

Comparative Example 1!

A first information recording medium was prepared in the same way as inExample 1 except that the resin material in Example 1 was replaced bythe same amount of a trifunctional acrylate (molecular weight/functionalgroup=179, manufactured by Toa Gosei Chemical Industry Co., Ltd.).

When an ITO film was formed to a thickness of 1,000 Å on the obtainedinformation recording layer by sputtering, the ITO film was cracked andcould not be used as an electrode layer. When information recording wascarried out by using this information recording medium in the same wayas in Example 3, the liquid crystal oozed out, making it difficult toeffect information recording.

Next, the third and fourth information recording mediums of the presentinvention will be explained.

FIG. 4(a) is a sectional view schematically showing the thirdinformation recording medium of the present invention. In the figure,reference numeral 3 denotes an information recording medium, 11 aninformation recording layer, 12 a resin layer, 13, 13" electrode layers,14 a photoconductive layer, and 15 a substrate. Each layer will beexplained below with reference to FIG. 4(a).

The electrode layers 13 and 13" and the substrate 15 must be transparentat either or both sides thereof. The electrode layer 13 and thesubstrate 15 may be the same as the electrode layer 13 and the substrate15 in the first information recording medium.

The electrode layer 13" on the side of the photoconductive layer 14 isformed of the same material and by the same method as in the case of theelectrode layer 13. When the electrode layer 13" is formed bysputtering, it is possible to control the injection of electric chargeinto the photoconductive layer 14 from the electrode layer 13" byheating the electrode layer 13" after it has been formed, and therebychanging the crystalline structure.

It should be noted that anti-reflection properties may be imparted tothe surface of the substrate 15 which is remote from the electrode layer13 by stacking a layer having anti-reflection effect, or by adjustingthe thickness of the transparent substrate to a level at whichanti-reflection effect is obtainable, or by combining together these twomeasures, according to need.

The photoconductive layer 14 may have a single-layer structure or adouble-layered structure including a charge generation layer and acharge transport layer, which are stacked in the mentioned order on theelectrode layer. The photoconductive layer generally functions such thatwhen it is irradiated with light, photocarriers (electrons or holes) aregenerated in the irradiated portion and these carriers are movableacross the width of the layer. The photoconductive layer exhibits theeffect particularly remarkably in the presence of an electric field. Itis particularly preferable for the photoconductive layer to have such afunction that an electric field, which is given to the informationrecording medium when the photoconductive layer is irradiated withlight, is amplified with time during the light irradiation, and evenafter the termination of the light irradiation, when the voltage iscontinuously applied, the photoconductive layer sustains the electricconductivity and continuously gives the electric field to theinformation recording medium.

A single-layer photoconductive layer is formed of an inorganic ororganic photoconductive substance. Examples of inorganic photoconductivesubstances include Se, Se--Te, ZnO, TiO₂, Si, CdS, etc. Such aninorganic photoconductive material is stacked on the electrode to alayer thickness of 5 μm to 30 μm, preferably 20 μm to 30 μm, by vapordeposition, sputtering, CVD, etc. It is also possible to form aphotoconductive layer by dispersing an inorganic photoconductivesubstance in the form of finely divided particles in an organicinsulating resin material, for example, a silicone resin, a polyesterresin, a polycarbonate resin, a styrene-butadiene resin, a styreneresin, a polyvinyl acetal resin, etc. In this case, it is preferable todisperse 0.1 to 10 parts by weight, preferably 1 to 5 parts by weight,of finely divided photoconductive particles in 1 part by weight of aresin material.

Organic photoconductive substances include dispersions of high- andlow-molecular photoconductive substances in an insulating binder.Examples of high-molecular photoconductive substances are polyvinylcarbazole (PVK), and poly-N-ethylenic unsaturated group-substitutedcarbazoles in which an ethylenic unsaturated group, e.g., allyl group oracryloxyalkyl group, is contained in place of the vinyl group in PVK.Examples of high-molecular photoconductive substances further includepoly-N-ethylenic unsaturated group-substituted phenothiazines, e.g.,poly-N-acrylphenothiazine, poly-N-(β-acryloxy)phenothiazine, etc., andpolyvinyl pyrene. Among these substances, poly-N-ethylenic unsaturatedgroup-substituted carbazoles, particularly polyvinyl carbazole maypreferably be employed.

Examples of low-molecular photoconductive substances are oxadiazolessubstituted by alkylaminophenyl group or the like, a triphenylmethanederivative, a hydrazone derivative, a butadiene derivative, a stilbenederivative, etc. It is also possible to form an organic photoconductivelayer having film-forming properties by dispersing 1 part by weight ofone selected from among the above low-molecular photoconductivesubstances in 0.1 to 5 parts by weight, preferably 0.1 to 1 part byweight, of an electrically insulating resin material, e.g., a siliconeresin, a polyester resin, a polycarbonate resin, a styrene-butadienecopolymer resin, a styrene resin, a polyvinyl acetal resin, etc.

An organic photoconductive layer produced by any of the above-describedmethods is formed on the electrode so that the dry film thickness is inthe range of 5 μm to 30 μm, preferably in the range of 10 μm to 30 μm.

In necessary, a persistent conductivity imparting agent as described inJapanese Patent Application No. 04-287983 (1992) may be added to theorganic photoconductive layer. Although the above-described organicphotoconductive layer per se has persistent conductivity, such apersistence conductivity imparting substance is added thereto for thepurpose of enhancing the persistent conductivity. A persistentconductivity imparting agent is added in the ratio of 0.001 to 1 part byweight, particularly 0.001 to 0.1 part by weight, to 1 part by weight ofan organic photoconductive substance. If the amount of persistentconductivity imparting agent added exceeds 1 part by weight, theamplifying function of the photoelectric sensor markedly lowers, whichis unfavorable. In some persistent conductivity imparting substances,the spectral sensitivity is not in the visible light region. Therefore,in a case where light information in the visible light region is used,an electron accepting substance, a sensitizing dye, etc. may be added tothe photoconductive layer in order to impart thereto sensitivity in thevisible light region. Examples of electron accepting substances usablefor this purpose are nitro-substituted benzene, diamino-substitutedbenzene, halogen-substituted benzene, quinones, and trinitrofluorenones.Examples of usable sensitizing dyes are a triphenyl methane dye, apyrylium salt dye, and a xanthene dye. An electron accepting substanceand a sensitizing dye are each added in the ratio of 0,001 to 1 part byweight, preferably 0.01 to 1 part by weight, to 1 part by weight of anorganic photoconductive substance. In a case where light information isin the infrared region, a pigment, e.g., phthalocyanine, or a pyrrole orcyanine dye should be added in an amount approximately equal to theabove. If the information light used is in the ultraviolet region or ashorter wavelength region, a light-absorbing substance appropriate forthe wavelength region concerned should be added in the same amount asthe above. Thus, the intended object can be attained.

A double-layered photoconductive layer is formed by successivelystacking a charge generation layer and a charge transport layer on theelectrode. This type of photoconductive layer includes an inorganicmaterial photoconductive layer and an organic material photoconductivelayer.

The charge generation layer in the inorganic material photoconductivelayer is formed on the electrode to a thickness of 0.05 μm to 1 μm byvapor deposition, sputtering, CVD, etc. using a material such as Se--Teor Si doped with sulfur or oxygen, for example. Then, a charge transportlayer is formed on the charge generation layer to a thickness of 10 μmto 50 μm in the same way as the above using a material such as Se, As₂,Se₃, Si, or Si doped with methane, for example.

The charge generation layer in the organic material photoconductivelayer is composed of a charge generating substance and a binder.Examples of charge generating substances usable in the present inventionare fluorenone azo pigments, monoazo pigments, bis-azo pigments, pyrrolepigments, azulenium salt pigments, phthalocyanine pigments, polycyclicaromatic pigments, pyrylium salt dyes, triazo pigments, squalium saltdyes, perylene pigments, anthanthrone pigments, cyanine pigments,polycyclic quinone pigments, and imidazole pigments. Specific examplesof charge generating substances usable in the present invention arethose which are described in Japanese Patent Application NO. 04-287983(1992).

Examples of binders usable in the present invention are a siliconeresin, a styrene-butadiene copolymer resin, an epoxy resin, an acrylicresin, a saturated or unsaturated polyester resin, a PMMA resin, a vinylchloride resin, a vinyl acetate resin, a vinyl chloride-vinyl acetateresin, etc. A charge generating substance selected from among thosementioned above is dispersed in one of these binders to form an organicmaterial charge generation layer. Preferable examples of chargegenerating substances are a fluorenone-azo pigment and a bis-azopigment. Preferable examples of binders are a polyester resin and avinyl chloride-vinyl acetate resin. It is preferable to mix 0.1 to 10parts by weight, preferably 0.1 to 1 part by weight, of a binder with 1part of a charge generating substance. The dry film thickness of thecharge generation layer is in the range of 0.01 μm to 1 μm, preferablyin the range of 0.1 μm to 0.3 μm.

The charge transport layer is composed of a charge transport substanceand a binder. The charge transport substance is a substance havingexcellent properties to transport electric charge generated in thecharge generation layer. Examples of charge transport substances usablein the present invention are hydrazone, pyrazoline, PVK carbazole,oxazole, triazole, aromatic amine, amine, triphenylmethane, butadiene,stilbene, and polycyclic aromatic compounds. The charge transportsubstance must have excellent hole transport properties. Preferablecharge transport substances are butadiene and stilbene compounds.Specific examples of charge transport substances are those which aredescribed in Japanese Patent Application No. 04-287983 (1992).

It is possible to use binders similar to those described above for thecharge generation layer. Preferable binders are a polyvinyl acetalresin, a styrene resin, a styrene-butadiene copolymer resin. It ispreferable to mix 0.1 to 10 parts by weight, more preferably 0.1 to 1part by weight, of a binder with 1 part of a charge transport substance.The dry film thickness of the charge transport layer is in the range of1 μm to 50 μm, preferably in the range of 10 μm to 30 μm.

Regarding the combination of charge generating and transport substances,it is preferable to combine together a fluorenone-azo pigment (chargegenerating substance) and a stilbene charge transport substance, and acombination of a bis-azo pigment (charge generating substance) and abutadiene or hydrazone charge transport substance.

Further, a persistent conductivity imparting agent and an electronaccepting substance as those described for the single-layerphotoconductive layer may be added to the charge generation andtransport layers in the double-layered photoconductive layer in the sameratios as the above. However, it is preferable to add them to the chargegeneration layer.

When an organic photoconductive layer is used to constitute theabove-described single-layer or double-layered photoconductive layer, itis preferable to use a coating solution prepared using as a solventdichloroethane, 1,1,2-trichloroethane, monochlorobenzene,tetrahydrofuran, cyclohexane, dioxane, 1,2,3-trichloropropane, ethylcellosolve, 1,1,1-trichloroethane, methyl ethyl ketone, chloroform,toluene, etc. The coating solution may be coated by blade coating,dipping, or spinner coating, for example.

The photoconductive layer may be provided on the electrode through acharge injection control layer. The charge injection control layer isprovided according to need to adjust the voltage practically applied tothe information recording medium by controlling the injection ofelectric charge into the photoconductive layer from the electrode 13. Inthe information recording medium of the present invention, thesensitivity of the photoconductive layer must be set in the operatingvoltage range of the liquid crystal in the information recording layer.The reason for this is that the difference (contrast potential) betweenthe potential (light potential) applied to the information recordinglayer in the exposed region and the potential (dark potential) appliedto the information recording layer in the unexposed region must be largein the operating range of the liquid crystal.

Accordingly, the dark potential applied to the liquid crystal layer inthe unexposed region of the photoconductive layer, for example, needs tobe set at the level of the operation initiating potential of the liquidcrystal. Therefore, the photoconductive layer is demanded to have anelectrical conductivity whereby a dark current of 10⁻⁴ to 10⁻⁸ A/cm²,preferably 10⁻⁵ to 10⁻⁶ A/cm², is induced when an electric field of 10⁵V/cm to 10⁶ V/cm is applied to the bulk layer of the photoconductivelayer. In a photoconductive layer in which the dark current induced isless than 10⁻⁸ A/cm², the molecules in the liquid crystal layer are notaligned even under exposure conditions. In a photoconductive layer inwhich a dark current of 10⁻⁴ A/cm² or more is induced, a large currentflows at the same time as the voltage application is initiated even in astate where no exposure light is applied, causing the liquid crystalmolecules in the information recording layer to be undesirably aligned.Consequently, no transmittance difference between the exposed andunexposed regions can be obtained even when exposure is carried out. Thecharge injection control layer is appropriately provided with relationto the above-described characteristics of the information recordingmedium. When the dark potential in the photoconductive layer needs to beheld down to a low level, the charge injection control layer is formedas a charge injection preventing layer. There are two types of chargeinjection preventing layer, that is, a layer that utilizes the tunneleffect, and a layer that utilizes rectifying effect. It is possible touse a charge injection preventing layer as described in Japanese PatentApplication No. 04-287983 (1992).

The information recording layer 11 that is provided on thephotoconductive layer 14 comprises a liquid crystal phase and a resinphase. It is possible to use the same liquid crystal materials as thosedescribed in connection with the first information recording medium.

As a material for forming the resin phase, it is possible to usethermosetting resin materials which are compatible with a solvent commonto the liquid crystal material, for example, an acrylic resin,methacrylic resin, polyester resin, polystyrene resin, copolymerscomposed mainly of these resin materials, epoxy resin, silicone resin,etc. Particularly preferable examples are ultraviolet curing resinmaterials which are compatible with a liquid crystal material or acommon solvent therewith in the form of a monomer or an oligomer.

Examples of such ultraviolet curing resin materials are acrylic andmethacrylic esters, i.e., multifunctional monomers and multifunctionalurethane and ester oligomers, e.g., dipentaerythritol hexaacrylate,trimethylolpropane triacrylate, polyethylene glycol diacrylate,polypropylene glycol diacrylate, isocyanuric acid (ethylene oxidemodified) triacrylate, dipentaerythritol pentaacrylate,dipentaerythritol tetraacrylate, neopentyl glycol diacrylate, hexanedioldiacrylate, etc., and monofunctional monomers or oligomers, e.g, nonylphenol modified acrylate, N-vinyl-2-pyrrolidone,2-hydroxy-3-phenoxypropyl acrylate, etc.

As to the solvent, any common solvent can be used, for example,hydrocarbon solvents represented by xylene, halogenated hydrocarbonsolvents represented by chloroform, alcohol derivative solventsrepresented by methyl cellosolve, and ether solvents represented bydioxane.

Examples of photo-curing agents usable in the present invention are thesame as those described above in connection with the first informationrecording medium.

It is preferable to use a liquid crystal and a resin material in such aratio that the liquid crystal content in the information recording layeris 10% to 90% by weight, more preferably 40% to 80% by weight. If theliquid crystal content is less than 10% by weight, light transmittanceis low even when the molecules in the liquid crystal phase are alignedby information recording, whereas, if the liquid crystal content exceeds90% by weight, the liquid crystal oozes out, causing unevenness of therecorded image. By allowing the information recording layer to contain arelatively large amount of liquid crystal, the contrast ratio can beimproved, and the operating voltage can be lowered.

In addition, by making the refractive indices of the liquid crystal andresin phases in the information recording layer approximately equal toeach other, the information recording layer can be selectively madeopaque and transparent as follows: When no electric field is appliedthereto, the information recording layer is opaque due to lightscattering, whereas, when an electric field is applied to theinformation recording layer, the molecules in the liquid crystal phaseare aligned, thus enabling the information recording region to becometransparent. No polarizer is needed when the recorded information isreproduced, and hence the optical system required for reading can besimplified.

The information recording layer is formed by a method wherein a mixedsolution of a resin material and a liquid crystal is coated on thephotoconductive layer by a coating method using a blade coater, a rollcoater or a spin coater, and then the resin material is cured. Ifnecessary, a leveling agent may be added to the mixed solution toimprove the coatability of the solution and to thereby obtain excellentsurface properties.

Further, a fluorocarbon surface-active agent may be added to the coatingsolution for the purpose of maintaining the wetting properties withrespect to the photoconductive layer and forming a skin layer made onlyof the resin material on the surface of the information recording layer.Examples of fluorocarbon surface-active agents usable for this purposeare the same as those described above in connection with the firstinformation recording medium. The fluorocarbon surface-active agent isused in the proportion of 0.1% to 20% by weight to the total amount ofliquid crystal and resin material used.

To coat the mixed solution of a resin material and a liquid crystal, itis necessary to completely dissolve the resin material and the liquidcrystal in each other by heating the solution at a temperature higherthan the temperature at which the liquid crystal maintains the isotropicphase. If the information recording layer is cured at a temperaturelower than the temperature at which the liquid crystal shows anisotropic phase, partial phase separation occurs between the liquidcrystal and the resin material, thus giving rise to problems. That is,the liquid crystal domain grows excessively, preventing a skin layerfrom being formed completely over the surface of the informationrecording layer, so that the liquid crystal will ooze out. In addition,the resin material is matted, so that it becomes difficult to take ininformation accurately. Further, there are cases where the resinmaterial cannot even retain the liquid crystal and hence no informationrecording layer is formed. When heating is required in order to maintainthe isotropic phase when the solvent is evaporated, particularly, thewetting properties with respect to the photoconductive layer lower,making it impossible to obtain a uniform information recording layer.

Particularly, when an ultraviolet curing resin is used as a resinmaterial, a skin layer having a thickness of about 0.6 μm is formed onthe surface of the resulting information recording layer. In addition,the use of an ultraviolet curing resin material makes it possible toform an information recording layer the inside of which has a structureincluding a liquid crystal phase which is filled with resin particleshaving a primary particle diameter of 0.03 μm to 0.6 μm. By virtue ofthe presence of the skin layer formed on the surface of the informationrecording layer, it is possible to increase the proportion of the liquidcrystal used in the information recording layer. In addition, it ispossible to suppress oozing of the liquid crystal to the surface of theinformation recording layer and hence possible to minimize the disorderof the image caused by the oozing of the liquid crystal.

Since the thickness of the information recording layer influences thedefinition of recorded information, it is preferable to set thethickness of the layer after it has been dried in the range of 0.1 μm to20 μm, more preferably 3 μm to 8 μm. By doing so, the operating voltagecan be lowered with the definition maintained at high level. If theinformation recording layer is excessively thin, the contrast of theinformation recording part becomes low, whereas, if the layer isexcessively thick, the operating voltage must be raised.

Next, a resin layer 12 is stacked on the information recording layer 11.The resin layer 11 is preferably formed by coating a thermoplastic resinfilm, a thermosetting resin film, an ionizing radiation curing resinfilm, e.g., an ultraviolet curing resin film, etc. It is also possibleto use an aqueous solution of polyvinyl alcohol, watersystempolyurethane, water glass, etc. as a water-soluble resin material whichis less compatible with an organic solvent and to coat such an aqueoussolution by a blade coater, a roll coater, or a spin coater. It is alsopossible to use a coating solution prepared by dissolving a resinmaterial, such as polytetrafluoroethylene, fluorinated ethylenepropylene, tetrafluoroethylene perfluoroalkyl vinyl ether copolymer,polyimide resin, polyether ketone resin, or poly-para-xylylene, in afluorine-containing solvent. Further, the resin layer 12 may also beformed by laminating a film of one of various kinds of polymer describedabove on the surface of the information recording layer 11 or bondingsuch a polymer film to the information recording layer surface throughan adhesive.

Particularly preferable examples of materials for forming the resinlayer 12 are polyethylene terephthalate, a multifunctional ultravioletcuring resin material, and polystyrene. With these resin materials, ahard coat layer having a high surface hardness can be obtained even whenit is in the form of a thin film. Thus, the durability of theinformation recording medium can be improved.

The resin layer 12 has a thickness of 0.01 μm to 40 μm, preferably 0.05μm to 5 μm. However, when the resin layer 12 is thick, the operatingvoltage applied to the liquid crystal phase during information recordinglowers. Therefore, it is necessary to raise the applied voltage in theinformation recording method of the present invention (described later).By stacking the resin layer 12 on the information recording layer 11, itis possible to prevent oozing of the liquid crystal from the surface ofthe information recording layer 11. In addition, it is possible tomaintain the electrical conductivity of the electrode layer 13 stackedon the resin layer 12 and to effect information recording free fromnoise or other problem.

Next, the electrode layer 13 is provided on the resin layer 12 using amaterial and a stacking method which are similar to those employed toform the above-described electrode layer 13". In this case, since theresin layer 12 has been formed, if an ITO film, for example, is stackedby vapor deposition, sputtering or other similar method, the ITO filmwill not be cracked, which would otherwise result in a lowering of theelectrical conductivity. A substrate similar to the above may be stackedon the electrode layer 13.

The information recording medium thus obtained is cut into anappropriate size in the width direction of the layers according to eachparticular use application. Accordingly, the interior of the informationrecording layer is exposed at each cut surface, so that the liquidcrystal phase may ooze out during storage. If the oozing phenomenonoccurs, accurate information recording cannot be effected at the endportions of the information recording medium. To prevent the occurrenceof this problem, it is preferable to stack a resin layer similar to theabove on each cut surface by coating or laminating after the informationrecording medium has been cut into an appropriate configuration, therebyprotecting the cut surfaces.

Next, the fourth information recording medium of the present inventionwill be explained.

FIG. 4(b) is a sectional view of the fourth information recording mediumaccording to the present invention, in which reference numeral 16denotes an insulating layer, and the same reference numerals as those inFIG. 4(a) denote the same contents.

The fourth information recording medium includes an insulating layer 16provided between the photoconductive layer 14 and the informationrecording layer 11 in the third information recording medium. Thisinformation recording medium is particularly suitable for an arrangementin which the photoconductive layer is an organic photosensitive layerformed by using a solvent. Thus, the insulating layer 16 is provided toprevent occurrence of unevenness of the recorded image which mightotherwise be caused by elution of the liquid crystal from theinformation recording layer by the interaction between thephotoconductive layer and the information recording layer if the latteris coated directly on the former, or elution of the photoconductivematerial by a solvent used for forming the information recording layer.

Accordingly, the material for forming the insulating layer 16 needs tobe incompatible with either of the materials for forming the organicphotoconductive layer and the information recording layer. If thematerial is electrically conductive, the space charge is diffused,causing deterioration of the resolution. Therefore, insulatingproperties are required. However, since the insulating layer lowers thevoltage distributed to the liquid crystal layer or degrades thedefinition, it is preferable for the layer thickness to be as small aspossible, preferably 2 μm or less. On the other hand, reduction in thelayer thickness gives rise to not only generation of information noisedue to the interaction that progresses with the passage of time but alsothe problem of permeation due to defects such as pinholes at the time ofcoating the material for stacking the layer. Since the permeabilitydepends on the proportion of the solid content of the material to becoated for stacking, the kind of solvent used and the viscosity, thelayer thickness is properly set in accordance with the material which isto be coated. When the voltage distribution to each layer is taken intoconsideration, it is preferable to use a material having a highdielectric constant as well as to minimize the layer thickness.

For example, the insulating layer is preferably formed by depositing aninorganic material, e.g., ZnO₂, MgF₂, SiO₂, TiO₂, CeO₂, Al₂ O₃, GeO₂,Si₃ N₄, AlN, TiN, etc., by vapor deposition, sputtering, chemical vapordeposition (CVD), etc. It is also possible to use an aqueous solution ofpolyvinyl alcohol, water-system polyurethane, polyvinyl pyrrolidine,polyacrylamide, water-soluble ultraviolet curing resin, water glass,etc. as a water-soluble resin material which is less compatible with anorganic solvent and to coat such an aqueous solution by spin coating,blade coating, roll coating and so forth. Further, a coatablefluorocarbon resin may also be used. In such a case, it may be dissolvedin a fluorine-containing solvent and coated by spin coating or stackedby blade coating, roll coating, etc. Coatable fluorocarbon resins whichare preferable to use include fluorocarbon resins disclosed in JapanesePatent Application No. 04-24722 (1992). When a coating type insulatingmaterial is used, it is necessary to select such a material that asolvent used therefor does not dissolve the photoconductive layer and itdoes not dissolve in a material constituting the information recordinglayer when formed by coating or in a solvent used when the informationrecording layer constituting material is coated.

In addition, if the insulating layer is formed of an organic materialwhich is formed into a film in a vacuum system, there is no likelihoodthat the material will dissolve the photoconductive layer during filmformation. Examples of materials usable for film formation by vapordeposition are polyethylene, polypropylene,poly(monochlorotrifluoroethylene), polytetrafluoroethylene, etc.Materials usable for film formation by CVD include poly-para-xylyleneand other materials which are described as specific examples in JapanesePatent Application No. 04-24722 (1992). It should be noted that there isno need to provide an insulating layer when the photoconductive layer isformed of an inorganic material and hence there is no interactionbetween the photoconductive layer and the information recording layer,such as oozing of the liquid crystal.

The third and fourth information recording mediums of the presentinvention are designed to record electrostatic information in a visibleform by the liquid crystal alignment. By properly selecting acombination of a liquid crystal and a resin material, these informationrecording mediums are endowed with memory effect that makes it possibleto retain information that has once been recorded in a visible form bythe liquid crystal alignment. The recorded information can be erased byheating the medium to a high temperature near the isotropic phasetransition temperature. Thus, the medium can be reused for informationrecording.

Next, the information recording and reproducing method for the third andfourth information recording mediums of the present invention will beexplained.

FIG. 5 is a view for explanation of the method of recording informationon the third information recording medium of the present invention. Itshould be noted that the information recording method for the fourthinformation recording medium is the same as that for the thirdinformation recording medium.

When information light 18 is incident on the information recordingmedium with a voltage applied between the electrodes 13 and 13',photocarriers are generated in the photoconductive layer 14 at theregion where the light is incident, and the photocarriers move by theaction of an electric field formed by the two electrodes 13 and 13',causing redistribution of the voltage. As a result, the molecules in theliquid crystal phase in the information recording layer 11 are alignedin the pattern of information light 18, thereby recording the desiredinformation. It should be noted that it is also possible to apply avoltage for a predetermined time with the information light 18 beingmade incident on the information recording medium.

In addition, since the operating voltage and its range differ amongliquid crystals, when the level of applied voltage and voltageapplication time are to be set, it is preferable to properly set thevoltage distribution in the information recording medium so that thevoltage distributed to the information recording layer will fall in theoperating voltage range of the liquid crystal used.

The information recording method of the present invention enables planaranalog recording and makes it possible to obtain recording at the liquidcrystal domain level and hence high resolution, and it also permits theexposure light pattern to be retained in the form of a visible image bythe molecular alignment in the liquid crystal phase.

To input information to the third and fourth information recordingmediums of the present invention, it is possible to adopt a methodsimilar to the above-described information input method for the firstinformation recording medium of the present invention.

Electrostatic information recorded on the third information recordingmedium may be reproduced by transmitted light, as shown in FIG. 6. Inthe information recording region, light A is transmitted because theliquid crystal molecules are aligned in the direction of the electricfield, whereas, in the region where no information has been recorded,light B is scattered, thus providing a contrast with the informationrecording region. Information that is recorded by the liquid crystalalignment is visible information which can be read by visual observationusing transmitted light, and it can also be read in the form of anenlarged image by using a projector. When laser scanning or CCD is usedto read the recorded information by transmitted light, the informationcan be read with high accuracy. It should be noted that occurrence ofscattered light can be prevented by using a Schlieren optical system, ifnecessary. The recorded information may be read by reflected light byuse of a reflecting film provided appropriately.

In a case whether the insulating layer 16 is a transparent insulatinglayer, electrostatic information recorded on the fourth informationrecording medium can be read by transmitted light in the same way asshown in FIG. 6. If the insulating layer is formed as a dielectricmirror layer, the recorded information can be read by reflected light.

The third and fourth information recording mediums of the presentinvention will be explained below more specifically by way of Example 5.In the Example, the term "parts" means parts by weight, and "%" meansper cent by weight.

EXAMPLE 5!

On a glass substrate having a thickness of 1.1 mm and thoroughlycleaned, an ITO film having a thickness of 1,000 Å was deposited by EBevaporation to obtain an electrode layer.

The surface of the electrode was coated with a coating solution in 0.4sec. by a spinner at 1,400 rpm. The coating solution was prepared bymixing 3 parts by weight of a fluorenone-azo pigment (manufactured byNikon Kanko Shikiso K.K.) having the following structure as a chargegenerating substance, 1 part by weight of a polyester resin material(Vylon 200, manufactured by Toyobo Co., Ltd.), 98 parts by weight of1,4-dioxane, and 98 parts by weight of cyclohexanone and shaking themixture for 6 hours in a paint shaker. ##STR3##

Thereafter, drying was carried out for 1 hour at 100° C. Thus, a chargegeneration layer having a thickness of 3,000 Å was stacked on theelectrode.

The surface of the charge generation layer was coated with a coatingsolution in 0.3 msec. by a spinner at 300 rpm. The coating solution wasprepared by mixing together 25 parts by weight of a para-dimethylstilbene having the following structure as a charge transport substance,5 parts by weight of a polystyrene resin material (HRM-3, manufacturedby Denki Kagaku Kogyo K.K.), 102 parts by weight of1,1,2-trichloroethane, and 68 parts by weight of dichloromethane.##STR4##

Thereafter, drying was carried out for 2 hours at 80° C., therebystacking a charge transport layer on the charge generation layer, andthus obtaining a photoelectric sensor having a photoconductive layer of20 μm in thickness which included charge generation and transportlayers.

Next, the surface of the photoconductive layer was coated by spinnercoating method (1500 rpm; 20 sec) with a solution of 4.5% a fluorocarbonresin (Cytop, manufactured by Asahi Glass Company, Ltd., having a waterabsorption of 0.01% and a resistivity of 1×10¹⁸ ohm-cm) inperfluoro(2-butyl tetrahydrofuran), and it was dried for 3 hours at 80°C., thereby obtaining a transparent insulating layer having a thicknessof about 0.8 μm.

Next, the surface of the transparent insulating layer was coated byusing a blade coater with a solution prepare by uniformly dissolving thefollowing constituent materials in 105 parts of xylene (special gradechemical, manufactured by Junsei Kagaku K.K.):

    ______________________________________                                        Multifunctional monomer     40    parts                                       (dipentaerythritol hexaacrylate, M-400, manufactured by                       Toa Gosei Chemical Industry Co., Ltd.,                                        molecular weight/functional group = 117)                                      Photo-curing initiator      2     parts                                       (2-hydroxy-2-methyl-1-phenylpropane-1-one, Darocure 1173,                     trade name, manufactured by Ciba-Geigy Ltd.)                                  Smectic liquid crystal      60    parts                                       (S-6, manufactured by BDH)                                                    Surface-active agent        3     parts                                       (Fluorad FC-430, trade name, manufactured by                                  Sumitomo 3M)                                                                  ______________________________________                                    

Immediately after the coating process, the wet coating was dried for 3minutes at 50° C. and then vacuum-dried for 3 minutes at 50° C.Immediately thereafter, the dry film was irradiated with UV light at 600mJ/cm² to cure the resin material, thereby preparing an informationrecording layer having a thickness of 6 μm. The information recordinglayer was white and opaque.

A cross-section of the information recording layer was dried after theliquid crystal was extracted with hot methanol, and then the internalstructure of the information recording layer was observed with ascanning electron microscope (S-800, manufactured by Hitachi, Ltd.;magnification of 10,000). As a result, it was revealed that the surfaceof the information recording layer was covered with the ultravioletcuring resin material having a thickness of 0.6 μm and the inside of thelayer was filled with resin particles having a particle diameter of 0.1μm.

Further, the surface of the information recording layer was coated byspin coating with a solution prepared by dissolving 1 part of aphoto-curing initiator (2-hydroxy-2-methyl-1-phenylpropane-1-one,Darocure 1173, trade name, manufactured by Ciba-Geigy Ltd.) in 10 partsof a multifunctional monomer (dipentaerythritol hexaacrylate, M-400,manufactured by Toa Gosei Chemical Industry Co., Ltd.). The coating wasirradiated with UV light at 300 mJ/cm² to form a resin layer having athickness of 1 μm.

When the pencil hardness of the information recording layer with theresin layer formed thereon was measured, it was 2H under a load of 1,000g. The pencil hardness of an information recording layer having no resinlayer stacked thereon was 2B. Thus, it was revealed that the hardness ofsuch an information recording layer was insufficient.

Next, an ITO film having a thickness of 500 Å was formed as atransparent electrode on the resin layer, thereby preparing a fourthinformation recording medium of the present invention.

Then, the information recording medium was subjected to exposure withthe photoconductive layer-side electrode used as a positive electrodeand the information recording layer-side electrode as a negativeelectrode. As a method of exposing the information recording medium,outdoor, daylight object photography was carried out using an ordinarycamera under the application of a voltage of 600 V with f=1.4 and ashutter speed of 1/60 sec. After the exposure, the information recordingmedium was taken out. It was possible to directly view a noiseless imagehaving gradation. In addition, the information recording medium was notdamaged when subjected to reading with a scanner using a CCD linesensor. Further, the read information was output by a sublimationtransfer printer. As a result, a hard copy with gradation and of highresolution was obtained.

As a comparative example, an information recording medium was preparedin the same way as the above-described fourth information recordingmedium except that the electrode layer was formed directly on theinformation recording layer without forming a resin layer. The surfaceof the information recording layer of this information recording mediumhad no sufficiently high hardness, and hence the medium was inferior instorage properties.

Next, the fifth and sixth information recording mediums of the presentinvention will be explained. FIG. 7(a) is a sectional view schematicallyshowing the fifth information recording medium of the present invention.In the figure, reference numeral 3 denotes an information recordingmedium, 11 an information recording layer, 13 an electrode layer, and 15a substrate.

The information recording layer 11 in the fifth information recordingmedium has a structure which includes a liquid crystal phase containinga dichroic dye, and a resin phase. It is possible to use the same liquidcrystal materials as those described for the first information recordingmedium.

It is preferable to select a dichroic dye which dissolves in the liquidcrystal used so as to be present in the liquid crystal phase and whichdoes not substantially dissolve in the resin material. The dichroic dyechanges its absorbance by the alignment of the dye molecular axes causedby the action of an electric field. Specific examples of dichroic dyesusable in the present invention include the following dichroic dyesmanufactured by Mitsui Toatsu Chemicals Inc.: SI=486 (maximum absorptionwavelength λ_(max) =406 nm in ZLI-1840, λ_(max) =397 nm in toluene; thesame is the case with the following dichroic dyes), SI-209 (λ_(max) =450nm, 432 nm), M-710 (λ_(max) =468 nm, 445 nm), M-570 (λ_(max) =451 nm,433 nm), M-361 (λ_(max) =477 nm, 474 nm), M-86 (λ_(max) =514 nm, 510 nm,λ_(max) =552 nm, 547 nm), M-370 (λ_(max) =519 nm, 514 nm, λ_(max) =555nm, 558 nm), SI-455 (λ_(max) =522 nm, 495 nm), SI-426 (λ_(max) =525 nm,504 nm), M-618 (λ_(max) =544 nm, 527 nm), SI-252 (λ_(max) =572 nm, 550nm), M-777 (λ_(max) =577 nm, 552 nm), S-432 (λ_(max) =575 nm, 552 nm),SI-512 (λ_(max) =587 nm, 580 nm), M-137 (λ_(max) =594 nm, 586 nm,(λ_(max) =639 nm, 623 nm), M-141 (λ_(max) =594 nm, 586 nm, (λ_(max) =639nm, 623 nm), M-483 (λ_(max) =594 nm, 586 nm, (λ_(max) =640 nm, 623 nm),M-412 (λ_(max) =593 nm, 585 nm, (λ_(max) =639 nm, 629 nm), M-34 (λ_(max)=593 nm, 585 nm, (λ_(max) =640 nm, 629 nm), SI-497 (λ_(max) =665 nm, 658nm), SI-501 (λ_(max) =675 nm, 665 nm), M-403 (λ_(max) =680 nm, 678 nm),S-344 (λ_(max) =598 nm, 510 nm), S-416 (λ_(max) =625 nm, 507 nm), S-426(λ_(max) =505 nm, 505 nm), S-428 (λ_(max) =505 nm, 508 nm, (λ_(max) =608nm, 530 nm, λ_(max) =587 nm, 574 nm, λ_(max) =632 nm, 622 nm), S-429(λ_(max) =486 nm, 486 nm, λ_(max) =540 nm, 534 nm, (λ_(max) =587 nm, 575nm, λ_(max) =632 nm, 620 nm), S-435 (λ_(max) =460 nm, 449 nm, λ_(max)=582 nm, 580 nm, λ_(max) =636 nm, 622 nm), and S-441 (λ_(max) =474 nm,467 nm, λ_(max) =589 nm, 583 nm, λ_(max) =633 nm, 620 nm).

It is also possible to use the following dichroic dyes manufactured byNippon Kayaku Co., Ltd.: LCD-102 (λ_(max) =645 nm in xylene; the same isthe case with the following dichroic dyes), LCD-105 (λ_(max) =680 nm),LCD-109 (λ_(max) =760 nm), LCD-116 (λ_(max) =670 nm), LCD-118 (λ_(max)=630 nm), LCD-121 (λ_(max) =630 nm), LCD-122 (λ_(max) =680 nm), LCD-204(λ_(max) =520 nm), LCD-208 (λ_(max) =530 nm), LCD-209 (λ_(max) =595 nm(550 nm)), LCD-211 (λ_(max) =595 nm (550 nm)), LCD-212 (λ_(max) =535 nm(575 nm)), LCD-213 (λ_(max) =585 nm), LCD-307 (λ_(max) =455 nm), etc.

In addition, it is also possible to use dichroic dyes manufactured byMitsubishi Chemical Industries, Ltd., i.e., Dye Nos. LSY-110, LSR-401,LSR-405, LSR-426, LSB-278, LSB-350, and LSB-335, and dichroic dyesmanufactured by Sumitomo Chemical Co., Ltd., i.e., Dye Nos. CLD-506,CLD-513, CLD-514, CLD-515, and CLD-516.

In the fifth information recording medium, it is preferable to use adichroic dye whose maximum absorption wavelength λ_(max) in toluene isin the range of 300 nm to 500 nm. It should be noted that in theinformation recording layer of the sixth information recording medium(described later), it is preferable to use a dichroic dye whose maximumabsorption wavelength λ_(max) in toluene is in the range of 600 nm to900 nm because it is useful to use the sixth information recordingmedium in the near-infrared region.

It is preferable to use a dichroic dye in the proportion of 0.001% to 5%by weight, more preferably 0.01% to 1% by weight, to the liquid crystal.If the amount of dichroic dye used is excessively large, although thecontrast is increased, the resistance of the medium lowers, making itimpossible to effectively apply a voltage to the liquid crystal phase.In addition, if the amount of dichroic dye added is excessively large,the amount of dye dissolving in the resin phase (described later)increases, so that the dichroic dye cannot effectively function. Theinformation recording layer in each of the fifth and sixth (describedlater) information recording mediums preferably has a volume resistivityof not lower than 1×1010 ohm-cm, more preferably not lower than 1×1011ohm-cm, at room temperature.

As a material for forming the resin phase, it is possible to use thesame resin materials described above in connection with the thirdinformation recording medium.

As to the solvent, any common solvent can be used. However, it ispreferable to use a solvent whose relative evaporation rate for n-butylacetate is smaller than 2, for example, hydrocarbon solvents representedby xylene, halogenated hydrocarbon solvents represented by chloroform,alcohol derivative solvents represented by methyl cellosolve, and ethersolvents represented by dioxane.

As a photo-curing agent, it is possible to use the same photo-curingagents described above in connection with the first informationrecording medium.

It is preferable to use a liquid crystal and a resin material in suchproportions that the liquid crystal content in the information recordinglayer is 10% to 90% by weight, more preferably 40% to 80% by weight. Ifthe liquid crystal content is less than 10% by weight, the contrastratio is low even when the molecules in the liquid crystal phase arealigned by information recording, whereas, if the liquid crystal contentexceeds 90% by weight, unfavorable phenomena such as oozing of theliquid crystal occur, causing unevenness of the recorded image.

The electrode layer 13 and the substrate 15 are formed by using the samematerials as those described above in connection with the firstinformation recording medium.

It should be noted that when the recorded information is reproduced bytransmitted light, the substrate 15 must be transparent. In such a case,anti-reflection properties may be imparted to the substrate by stackinga layer having anti-reflection effect on the surface of the substrate 15which is remote from the electrode layer 13, or by adjusting thethickness of the transparent substrate to a level at whichanti-reflection effect is obtainable, or by combining together these twomeasures, according to need.

The information recording layer is formed by coating a mixed solutioncontaining a resin material, a liquid crystal and a dichroic dye on theelectrode and then curing the coated material. A fluorocarbonsurface-active agent may be added to the mixed solution for the purposeof maintaining the wetting properties with respect to the electrodelayer and forming a skin layer made only of the resin material on thesurface of the information recording layer. Examples of fluorocarbonsurface-active agents usable for this purpose are the same as thosedescribed above in connection with the first information recordingmedium. The fluorocarbon surface-active agent is used in the proportionof 0.1% to 20% by weight to the total amount of liquid crystal, resinmaterial and dichroic dye used. If necessary, a leveling agent may beadded to the mixed solution to improve the coatability of the solutionand to thereby obtain excellent surface properties.

The information recording layer is formed by the same method as thatemployed to form the information recording layer of the firstinformation recording medium except that the a dichroic dye is containedin the coating solution.

Next, a method of recording information on the fifth informationrecording medium of the present invention will be explained.

Information recording may be effected by using a photoelectric sensor,heat, laser, corona charging or other similar recording method. However,it is preferable to effect information recording by using aphotoelectric sensor. It is possible to use the same photoelectricsensor as that used to effect information recording on the firstinformation recording medium.

The system for recording information on the first information recordingmedium, which incorporates a photoelectric sensor, is similar to theinformation recording system for the first information recording medium,which is shown in FIG. 2. The information input method is also similarto that for the first information recording medium.

Electrostatic information recorded on the information recording mediumis reproduced by a method similar to the method of reproducinginformation from the first information recording medium. Wheninformation is reproduced by transmitted light, as shown in FIG. 3, inthe information recording region, light A is transmitted because theliquid crystal and the dichroic dye are aligned in the direction of theelectric field, whereas, in the region where no information has beenrecorded, light B is scattered, thus providing a contrast with theinformation recording region. Since the information recording layercontains a dichroic dye, the reproduced information is superior incontrast. Information that is recorded by the liquid crystal alignnmentis visible information which can be read by visual observation usingtransmitted light, and it can also be read in the form of an enlargedimage by using a projector. When laser scanning or CCD is used to readthe recorded information by transmitted light, the information can beread with high accuracy. It should be noted that occurrence of scatteredlight can be prevented by using a Schlieren optical system, ifnecessary. It is also possible to read the recorded information byreflected light. When the contrast is a matter of great concern, areflecting layer should be provided on any of the layers.

Next, the sixth information recording medium of the present inventionwill be explained. The sixth information recording medium is formed byincorporating a photoconductive layer into the fifth informationrecording medium of the present invention. It does not need aphotoelectric sensor or the like for information recording, but theinformation recording medium is capable of information recording byitself.

FIG. 7(b) is a sectional view schematically showing the sixthinformation recording medium. In the figure, reference numeral 3 denotesan information recording medium, 11 an information recording layer, 13and 13" electrode layers, 14 a photoconductive layer, and 15 asubstrate.

The electrode layer 13" and the photoconductive layer 14 are similar tothe electrode layer 13" and the photoconductive layer 14, which havebeen described in connection with the third information recordingmedium. Either or both sides of each of the electrode layers 13, 13" andthe substrate 15 must be transparent.

Further, the arrangement may be such that the photoconductive layer 14is provided on the electrode layer 13" through a charge injectioncontrol layer in the same way as in the case of the third informationrecording medium.

Next, the information recording layer 11, which is similar to thatdescribed in connection with the third information recording medium, isstacked on the photoconductive layer 14 in the same way as in the caseof the third information recording medium.

It should be noted that since the information recording layer of thesixth information recording medium is free from oozing of the liquidcrystal from the information recording layer surface, the electrodelayer 13 can be formed directly on the information recording layersurface by sputtering. Thus, it is possible to form an electrode layerwhich is free from a lowering of the electrical conductivity.

The electrode layer 13 may be formed by using a material similar to thatused for the electrode layer of the first information recording medium.Since the surface of the information recording layer is formed with askin layer made only of a resin material, if an ITO film, for example,is stacked to a thickness of 1,000 Å by sputtering or other similarmethod, it is possible to form an electrode which will not be cracked.It should be noted that a substrate may be stacked on the electrode 13.

Further, in the sixth information recording medium a transparentinsulating layer, which is similar to the transparent insulating layerdescribed in connection with the fourth information recording medium,may be provided between the photoconductive layer 14 and the informationrecording layer 11. Alternatively, a dielectric mirror layer may beprovided.

The information recording and reproducing method for the sixthinformation recording medium of the present invention will be explained.FIG. 8 is a view for explanation of the method of recording informationon the sixth information recording medium of the present invention.

When information light 18 is incident on the information recordingmedium with a voltage applied between the electrodes 13 and 13',photocarriers are generated in the photoconductive layer 14 at theregion where the light is incident, and the photocarriers move by theaction of an electric field formed by the two electrodes 13 and 13',causing redistribution of the voltage. As a result, the liquid crystalphase and the dichroic dye in the information recording layer 11 arealigned in the pattern of information light 18, thereby recording thedesired information. It should be noted that it is also possible toapply a voltage for a predetermined time with the information light 18being made incident on the information recording medium.

In addition, since the operating voltage and its range differ amongliquid crystals, when the level of applied voltage and voltageapplication time are to be set, it is preferable to properly set thevoltage distribution in the information recording medium so that thevoltage distributed to the information recording layer will fall in theoperating voltage range of the liquid crystal used.

The information recording method of the present invention enables planaranalog recording and makes it possible to obtain recording at the liquidcrystal particle level and hence high resolution, and it also permitsthe exposure light pattern to be retained in the form of a visible imageby the molecular alignment in the liquid crystal phase.

To input information to this information recording medium, it ispossible to adopt a method similar to the above-described informationinput method for the first information recording medium of the presentinvention. The information recorded on the sixth information recordingmedium may be reproduced by a method similar to that in the case of thethird information recording medium, which is shown in FIG. 6.

The fifth and sixth information recording mediums are cut into anappropriate size in the width direction of the layers according to eachparticular use application. Accordingly, the interior of the informationrecording layer is exposed at each cut surface, so that the liquidcrystal phase may ooze out during storage. If the oozing phenomenonoccurs, accurate information recording cannot be effected at the endportions of the information recording medium. To prevent the occurrenceof this problem, it is preferable to stack a resin layer similar to theabove on each cut surface by coating or laminating after the informationrecording medium has been cut into an appropriate configuration, therebyprotecting the cut surfaces.

The fifth and sixth information recording mediums are designed to recordelectrostatic information in a visible form by the liquid crystalalignment. By properly selecting a combination of a liquid crystal and aresin material, these information recording mediums are endowed withmemory effect that makes it possible to retain information that has oncebeen recorded in a visible form by the liquid crystal alignment. Therecorded information can be erased by heating the medium to a hightemperature near the isotropic phase transition temperature. Thus, themedium can be reused for information recording.

The fifth and sixth information recording mediums of the presentinvention will be explained below more specifically by way of Examples 6to 10 and Comparative Examples 2 and 3. In these Examples, the term"parts" means parts by weight, and "%" means per cent by weight.

EXAMPLE 6!

The following constituent materials were dissolved in xylene (specialgrade chemical, manufactured by Junsei Kagaku K.K.) to prepare a 50%coating solution:

    ______________________________________                                        Smectic liquid crystal     5      parts                                       (S-6, manufactured by Merck & Co., Ltd.)                                      Nematic liquid crystal     0.5    parts                                       (E-31LV, manufactured by Merck & Co., Ltd.)                                   Ultraviolet curing resin   4.5    parts                                       (M-400, manufactured by Toa Gosei Chemical Industry                           Co., Ltd.)                                                                    Photo-curing initiator     0.25   parts                                       (Darocure 1173, manufactured by Ciba-Geigy Ltd.)                              Dicbroic dye               0.01   parts                                       (SI-486 (azo dye), manufactured by Mitsui Toatsu                              Chemicals Inc.)                                                               Surface-active agent       0.1    parts                                       (Fluorad FC-430, manufactured by Sumitomo 3M)                                 ______________________________________                                    

The resulting solution was coated by using a spinner (10 sec.; 300 rpm)on the electrode side of a glass substrate (1.1 mm in thickness) havingan ITO electrode formed thereon to a thickness of 1,000 Å by sputtering.The glass substrate thus coated was allowed to stand for 3 minutes in avacuum dryer at 47° C. Thereafter, the vacuum dryer was evacuated for 2minutes and then returned to the normal pressure state, thereby removingthe solvent.

Next, the dry film was irradiated with ultraviolet rays at 600 mJ/cm² tocure the resin material, thereby preparing an information recordingmedium having an information recording layer of 6 μm in thickness. Thetransmittance of the medium at 600 nm was 38%, and the volumeresistivity at room temperature was 2×10¹¹ ohm-cm.

A cross-section of the information recording layer was dried after theliquid crystal was extracted with hot methanol, and then the internalstructure of the information recording layer was observed with ascanning electron microscope (S-800, manufactured by Hitachi, Ltd.;magnification of 10,000). As a result, it was revealed that the surfaceof the information recording layer was covered with the ultravioletcuring resin material having a thickness of 0.6 μm and the inside of thelayer had a structure in which the liquid crystal phase that formed acontinuous layer was filled with the resin particle phase having aparticle diameter of 0.1 μm.

EXAMPLE 7!

The following constituent materials were dissolved in xylene (specialgrade chemical, manufactured by Junsei Kagaku K.K.) to prepare a 50%coating solution:

    ______________________________________                                        Smectic liquid crystal     5      parts                                       (S-6, manufactured by Merck Co., Ltd.)                                        Nematic liquid crystal     0.5    parts                                       (E-31LV, manufactured by Merck & Co., Ltd.)                                   Ultraviolet curing resin   4.5    parts                                       (M-400, manufactured by Toa Gosei Chemical Industry                           Co., Ltd.)                                                                    Photo-curing initiator     0.25   parts                                       (Darocure 1173, manufactured by Ciba-Geigy Ltd.)                              Dichroic dye               0.01   parts                                       (M-34 (anthraquinone dye.), manufactured by Mitsui                            Toatsu Chemicals Inc.)                                                        Surface-active agent       0.1    parts                                       (Fluorad FC-430, manufactured by Sumitomo 3M)                                 ______________________________________                                    

The resulting solution was coated by using a spinner (10 sec.; 300 rpm)on the electrode side of a glass substrate (1.1 mm in thickness) havingan ITO electrode formed thereon to a thickness of 1,000 Å by sputtering.The glass substrate thus coated was allowed to stand for 3 minutes in avacuum dryer at 47° C. Thereafter, the vacuum dryer was evacuated for 2minutes and then returned to the normal pressure state, thereby removingthe solvent.

Next, the dry film was irradiated with ultraviolet rays at 600 mJ/cm² tocure the resin material, thereby preparing an information recordingmedium having an information recording layer of 6 μm in thickness. Thetransmittance of the medium at 600 nm was 42%, and the volumeresistivity at room temperature was 2×1011 ohm-cm.

EXAMPLE 8!

The following constituent materials were dissolved in xylene (specialgrade chemical, manufactured by Junsei Kagaku K.K.) to prepare a 50%coating solution:

    ______________________________________                                        Smectic liquid crystal     5      parts                                       (S-6, manufactured by Merck & Co., Ltd.)                                      Nematic liquid crystal     0.5    parts                                       (E-31LV, manufactured by Merck & Co., Ltd.)                                   Ultraviolet curing resin   4.5    parts                                       (M-400, manufactured by Toa Gosei Chemical Industry                           Co., Ltd.)                                                                    Photo-curing initiator     0.25   parts                                       (Darocure 1173, manufactured by Ciba-Geigy Ltd.)                              Dichroic dye               0.03   parts                                       (SI-486 (azo dye), manufactured by Mitsui Toatsu                              Chemicals Inc.)                                                               Surface-active agent       0.1    parts                                       (Fluorad FC-430, manufactured by Sumitomo 3M)                                 ______________________________________                                    

The resulting solution was coated by using a spinner (10 sec.; 300 rpm)on the electrode side of a glass substrate (1.1 mm in thickness) havingan ITO electrode formed thereon to a thickness of 1,000 Å by sputtering.The glass substrate thus coated was allowed to stand for 3 minutes in avacuum dryer at 47° C. Thereafter, the vacuum dryer was evacuated for 2minutes and then returned to the normal pressure state, thereby removingthe solvent.

Next, the dry film was irradiated with ultraviolet rays at 600 mJ/cm² tocure the resin material, thereby preparing an information recordingmedium having an information recording layer of 6 μm in thickness. Thetransmittance of the medium at 600 nm was 25%, and the volumeresistivity at room temperature was 1×10¹¹ ohm-cm.

Comparative Example 2!

The following constituent materials were dissolved in xylene (specialgrade chemical, manufactured by Junsei Kagaku K.K.) to prepare a 50%coating solution:

    ______________________________________                                        Smectic liquid crystal     5      parts                                       (S-6, manufactured by Merck & Co., Ltd.)                                      Nematic liquid crystal     0.5    parts                                       (E-31LV, manufactured by Merck & Co., Ltd.)                                   Ultraviolet curing resin   4.5    parts                                       (M-400, manufactured by Toa Gosei Chemical Industry                           Co., Ltd.)                                                                    Photo-curing initiator     0.25   parts                                       (Darocure 1173, manufactured by Ciba-Geigy Ltd.)                              Surface-active agent       0.1    parts                                       (Fluorad FC-430, manufactured by Sumitomo 3M)                                 ______________________________________                                    

The resulting solution was coated by using a spinner (10 sec.; 300 rpm)on the electrode side of a glass substrate (1.1 mm in thickness) havingan ITO electrode formed thereon to a thickness of 1,000 Å by sputtering.The glass substrate thus coated was allowed to stand for 3 minutes in avacuum dryer at 47° C. Thereafter, the vacuum dryer was evacuated for 2minutes and then returned to the normal pressure state, thereby removingthe solvent.

Next, the dry film was irradiated with ultraviolet rays at 600 mJ/cm² tocure the resin material, thereby preparing an information recordingmedium having an information recording layer of 6 μm in thickness. Thetransmittance of the medium at 600 nm was as high as 46%, although thevolume resistivity at room temperature was 2×10¹¹ ohm-cm. Thus, it willbe understood that when no dichroic dye is contained, the transmittancebecomes high.

Comparative Example 3!

The following constituent materials were dissolved in xylene (specialgrade chemical, manufactured by Junsei Kagaku K.K.) to prepare a 50%coating solution:

    ______________________________________                                        Smectic liquid crystal     5      parts                                       (S-6, manufactured by Merck & Co., Ltd.)                                      Nematic liquid crystal     0.5    parts                                       (E-31LV, manufactured by Merck & Co., Ltd.)                                   Ultraviolet curing resin   4.5    parts                                       (M-400, manufactured by Toa Gosei Chemical Industry                           Co., Ltd.)                                                                    Photo-curing initiator     0.25   parts                                       (Darocure 1173, manufactured by Ciba-Geigy Ltd.)                              Dichroic dye               1      part                                        (SI-486 (azo dye), manufactured by Mitsui Toatsu                              Chemicals Inc.)                                                               Surface-active agent       0.1    parts                                       (Fluorad FC-430, manufactured by Sumitomo 3M)                                 ______________________________________                                    

The resulting solution was coated by using a spinner (10 sec.; 300 rpm)on the electrode side of a glass substrate (1.1 mm in thickness) havingan ITO electrode formed thereon to a thickness of 1,000 Å by sputtering.The glass substrate thus coated was allowed to stand for 3 minutes in avacuum dryer at 47° C. Thereafter, the vacuum dryer was evacuated for 2minutes and then returned to the normal pressure state, thereby removingthe solvent.

Next, the dry film was irradiated with ultraviolet rays at 600 mJ/cm² tocure the resin material, thereby preparing an information recordingmedium having an information recording layer of 6 μm in thickness. Thetransmittance of the medium at 600 nm was 10%, but the volumeresistivity at room temperature was as low as 5×10⁸ ohm-cm. Thus, itwill be understood that the volume resistivity lowers as the amount ofdichroic dye used increases.

EXAMPLE 9!

The photoelectric sensor prepared in Example 4 and the informationrecording medium prepared in Example 6 were disposed to face each otheracross an air gap of 10 μm defined by a spacer 19 of polyimide film,thereby forming a stack structure.

In an information recording system incorporating the stack structure,which was similar to that shown in FIG. 2, a DC voltage of 850 V wasapplied between the respective electrodes of the photoelectric sensorand the information recording medium for 0.05 sec., and at the sametime, exposure was carried out by projecting a gray scale from thephotoelectric sensor side for 1/30 sec. with an imaging camera (RB67,manufactured by Mamiya Camera Co., Ltd.). After the exposure, theinformation recording medium was taken out. When the informationrecording medium was observed by transmitted light, the transmittance inthe light-transmitting portions was 90%, and record regions comprisingthe light-transmitting portions corresponding to the gray scale wereobserved.

Next, the information recorded on the information recording medium wasread with a film scanner (LS-3500, manufactured by Nikon Corporation),and the read information was output by using a sublimation transferprinter (SP-5500, manufactured by JVC). As a result, a favorable printcorresponding to the gray scale was obtained.

EXAMPLE 10!

On a glass substrate having a thickness of 1.1 mm and thoroughlycleaned, an ITO film having a thickness of 1,000 Å was deposited by EBevaporation to obtain an electrode layer.

The surface of the electrode was coated with a coating solution by usinga blade coater having a gap of 2 mil. The coating solution was preparedas follows: 3 parts by weight of a fluorenone-azo pigment (manufacturedby Nihon Kanko Shikiso K.K.) having the following structure as a chargegenerating substance and 1 part by weight of a polyester resin material(Vylon 200, manufactured by Toyobo Co., Ltd.) were thoroughly dispersedin a paint shaker with a mixed solvent comprising 1,4-dioxane andcyclohexane in the ratio of 1:1 to prepare a 100 g solution in which thesolid matter content was 2% by weight: ##STR5##

Thereafter, drying was carried out for 1 hour at 100° C. Thus, a chargegeneration layer having a thickness of 0.3 μm was stacked on theelectrode.

The surface of the charge generation layer was coated with a coatingsolution by using a blade coater. The coating solution was prepared bymixing together 25 parts by weight of a para-dimethyl stilbene havingthe following structure as a charge transport substance, 5 parts byweight of a polystyrene resin material (HRM-3, manufactured by DenkiKagaku Kogyo K.K.), 102 parts by weight of 1,1,2-trichloroethane, and 68parts by weight of dichloromethane. ##STR6##

Thereafter, drying was carried out for 2 hours at 80° C., therebystacking a charge transport layer on the charge generation layer, andthus providing a photoconductive layer of 20 μm in thickness whichincluded charge generation and transport layers.

Next, the surface of the photoconductive layer was coated by a spinner(1500 rpm; 20 sec) with a solution of 4.5% a fluorocarbon resin (Cytop,trade name, manufactured by Asahi Glass Company, Ltd., having a waterabsorption of 0.01% and a resistivity of 1×10¹⁸ ohm-cm) inperfluoro(2-butyl tetrahydrofuran), and it was dried for 1 hour at 80°C., thereby obtaining a transparent insulating layer having a thicknessof 0.8 μm.

Next, the surface of the transparent insulating layer was coated byusing a spinner (10 sec.; 300 rpm) with a 50% coating solution preparedby dissolving the following constituent materials in xylene (specialgrade chemical, manufactured by Junsei Kagaku K.K.):

    ______________________________________                                        Smectic liquid crystal     5      parts                                       (S-6, manufactured by Merck & Co.1 Ltd.)                                      Nematic liquid crystal     0.5    parts                                       (E-31LV, manufactured by Merck & Co., Ltd.)                                   Ultraviolet curing resin   4.5    parts                                       (M-400; manufactured by Toa Gosei Chemical Industry                           Co., Ltd.)                                                                    Photo-curing initiator     0.25   parts                                       (Darocure 1173, manufactured by Ciba-Geigy Ltd.)                              Dichroic dye               0.01   parts                                       (M-403 (anthraquinone dye), manufactured by Mitsui                            Toatsu Chemicals Inc.)                                                        Surface-active agent       0.1    parts                                       (Fluorad PC-430, manufactured by Sumitomo 3M)                                 ______________________________________                                    

The glass substrate thus coated was allowed to stand for 3 minutes in avacuum dryer at 47° C. Thereafter, the vacuum dryer was evacuated for 2minutes and then returned to the normal pressure state, thereby removingthe solvent. Next, the dry film was irradiated with ultraviolet rays at600 mJ/cm² to cure the resin material, thereby stacking an informationrecording layer of 6 μm in thickness on the transparent insulatinglayer.

Next, an ITO film having a thickness of 500 Å was formed as an upperelectrode on the information recording layer by sputtering, therebypreparing a sixth information recording medium according to the presentinvention. The transmittance of the information recording medium forlight of 800 nm was 60%.

As a comparative example, an information recording medium was preparedin the same way as the above except that no dichroic dye was addedthereto. The transmittance of this information recording medium forlight of 800 nm was 64%. Thus, it will be understood that thetransmittance is high when no dichroic dye is added to the medium.

The information recording medium thus formed was subjected to exposure,as shown in FIG. 8. With a DC voltage of 600 V applied between thephotoconductive layer-side electrode as a positive electrode and theinformation recording layer-side electrode as a negative electrode,exposure was carried out for 0.1 sec. from the photoconductive layerside by using a 1,000 lux halogen lamp as a light source. After theexposure, the information recording medium was taken out.

After the information recording, the transmittance for light of 800 nmwas 90%. Similar information recording was carried out for aninformation recording medium having no dichroic dye added thereto, andthe transmittance for light of 800 nm was similarly measured. Thetransmittance of this information recording medium was 90%. However, itwill be clear from comparison between the transmittances of these twoinformation recording mediums before the information recording that theinformation recording medium of the present invention has a highercontrast than that of the information recording medium having nodichroic dye added thereto.

What we claim is:
 1. An information recording medium comprising anelectrode layer and an information recording layer provided on saidelectrode layer, wherein said information recording layer is formed bycoating a surface of said electrode layer with a mixed solutioncontaining a multifunctional ultraviolet curing resin material, whoseparameter, expressed by an average molecular weight divided by anaverage number of functional groups, is not greater than 160, afluorocarbon surface-active agent, a liquid crystal and a dichroic dye,and then curing said coating by irradiation with ultraviolet rays, saiddichroic dye being soluble in said liquid crystal but substantiallyinsoluble in an ultraviolet curing resin phase.
 2. An informationrecording medium according to claim 1, wherein said dichroic dye hasλ_(max) of 300 nm to 500 nm in toluene.
 3. An information recordingmedium comprising a first electrode layer, a photoconductive layer, aninformation recording layer and a second electrode layer, which aresuccessively provided one on top of another, wherein at least one ofsaid first electrode layer or second electrode layer is transparent, andwherein said information recording layer is formed by coating a mixedsolution containing a multifunctional ultraviolet curing resin material,whose parameter, expressed by an average molecular weight divided by anaverage number of functional groups, is not greater than 160, afluorocarbon surface-active agent, a liquid crystal, and a dichroic dyeon said first electrode layer, and then curing the coated mixed solutionby irradiation with ultraviolet rays, said dichroic dye being soluble insaid liquid crystal but substantially insoluble in an ultraviolet curingresin phase.
 4. An information recording medium according to claim 3,wherein said dichroic dye has λ_(max) of 400 nm to 900 nm in toluene. 5.An information recording medium according to claim 1 or 3, wherein saiddichroic dye phase is formed from an amount in the range of 0.01% to 5%by weight.
 6. An information recording medium comprising an electrodelayer and an information recording layer provided on said electrodelayer, said information recording layer being formed by coating a mixedsolution containing a multifunctional ultraviolet curing resin material,whose parameter, expressed by an average molecular weight divided by anaverage number of functional groups, is not greater than 160, afluorocarbon surface-active agent, a liquid crystal, and a dichroic dyeon said electrode layer, and then curing the coated mixed solution byirradiation with ultraviolet rays so that a skin layer of saidultraviolet curing resin material is formed on an outer surface of saidinformation recording layer, said dichroic dye being soluble in saidliquid crystal but substantially insoluble in an ultraviolet curingresin phase.
 7. An information recording material according to claim 6,wherein said dichroic dye has a λ_(max) at 300 nm to 500 nm in toluene.8. An information recording medium comprising a first electrode layer, aphotoconductive layer, an information recording layer, and a secondelectrode layer, which are successively provided one on top of another,wherein at least one of said first electrode layer or second electrodelayer is transparent; and wherein said information recording layer isformed by coating a mixed solution containing a multifunctionalultraviolet curing resin material, whose parameter, expressed by anaverage molecular weight divided by an average number of functionalgroups, is not greater than 160, a fluorocarbon surface-active agent, aliquid crystal, and a dichroic dye on said first electrode layer, andthen curing the coated mixed solution by irradiation with ultravioletrays, so that a skin layer of said ultraviolet curing resin material isformed on an outer surface of said information recording layer, saiddichroic dye being soluble in said liquid crystal but substantiallyinsoluble in an ultraviolet curing resin phase.
 9. An informationrecording medium according to claim 8, wherein said dichroic dye hasλ_(max) at 400 nm to 900 nm in toluene.
 10. An information recordingmedium according to claim 6 or 8, wherein said dichroic dye is containedin an amount of from 0.01% to 5% by weight.
 11. An information recordingmedium comprising an electrode layer and an information recording layerprovided on said electrode layer, wherein said information recordinglayer is formed by coating a mixed solution containing a multifunctionalultraviolet curing resin material, whose parameter, expressed by anaverage molecular weight divided by an average number of functionalgroups, is not greater than 160, a fluorocarbon surface-active agent, aliquid crystal, and a dichroic dye on said electrode layer, and thencuring the coated mixed solution by irradiation with ultraviolet rays sothat a skin layer of said ultraviolet curing resin material is formed onan outer surface of said information recording layer, and saidinformation recording layer has an internal structure in which a liquidcrystal continuous phase is filled with particles of said ultravioletcuring resin material, said dichroic dye being soluble in said liquidcrystal but substantially insoluble in an ultraviolet curing resinphase.
 12. An information recording medium according to claim 11,wherein said dichroic dye has λ_(max) at 300 nm to 500 nm in toluene.13. An information recording medium comprising a first electrode layer,a photoconductive layer, an information recording layer, and a secondelectrode layer, which are successively provided one on top of another,wherein at least one of said first electrode layer or second electrodelayer is transparent; and wherein said information recording layer isformed by coating a mixed solution containing a multifunctionalultraviolet curing resin material, whose parameter, expressed by anaverage molecular weight divided by an average number of functionalgroups, is not greater than 160, a fluorocarbon surface-active agent, aliquid crystal, and a dichroic dye on said first electrode layer, andthen curing the coated mixed solution by irradiation with ultravioletrays so that a skin layer of said ultraviolet curing resin material isformed on an outer surface of said information recording layer, and saidinformation recording layer has an internal structure in which a liquidcrystal continuous phase is filled with particles of said ultravioletcuring resin material, said dichroic dye being soluble in said liquidcrystal but substantially insoluble in an ultraviolet curing resinphase.
 14. An information recording medium according to claim 13,wherein said dichroic dye has λ_(max) at 400 nm to 900 nm in toluene.15. An information recording medium according to claim 11 or 13, whereinsaid dichroic dye is contained in an amount of from 0.01% to 5% byweight.